"What people don't realise is it's a form of bereavement. There were days I couldn't get out of bed. I just couldn't face the world."
Nicci Fletcher, 50, says she and her husband Andrew felt "real grief" at not having children together and wanted to help other people going through the same experience.
So they decided to set up an online subscription magazine aimed solely at other people who wanted children but couldn't have them.
Nicci and Andrew met in their late 30s. When an unplanned pregnancy ended in miscarriage they were devastated but thought they would be able to conceive again.
But Nicci later discovered she had inherited her mother's endometriosis - a condition which can lead to infertility.
"My mother was advised not to have any more children after me but I'd never asked why," she said. "I kick myself now. I had no symptoms at all. My periods were like clockwork, no pain.
"If I'd known then I could have done something about it. I could have had my eggs harvested and frozen. When you're in your 20s, you think you've got all the time in the world."
Childlessness on the rise
According to government statistics published in November, nearly one in five women in England and Wales born in 1971 have no children at all - compared to one in 10 of their mother's generation.
Although there are no official statistics on how many childless women wanted children, an academic study from Erasmus University Rotterdam in the Netherlands suggested it could be as high as 90%.
The situation hit Nicci hard. As well as the pain of not having children, she felt isolated from her friends who were busy with their young families.
"Of my 20 close friends, I was the only one without a child," she said. "I had such a feeling of being marginalised.
"They were supportive as much as they could be supportive but we were in denial, we didn't ask for any support."
Andrew, 52, became despondent at not being able to resolve the situation.
"It's different for men. We don't have the biological imperative that women do - we can supposedly have babies at any age," he said.
"But I felt depressed at not being able to help Nicci. I can say the right words, I can rub her back but I can't fix it. Most blokes like to fix things."
- Is flexible working biased against non-parents?
- Soaring childlessness among southern European women - report
- When childless isn't a choice
He also grieved for the future he had planned.
"We bought our farmhouse in France because it would be a marvellous place to bring up children. As a couple you make decisions based on the assumption of having children. It's painful realising you're not going to have the life you expected."
Slowly, Nicci and Andrew began to withdraw from friends and family.
"I'd always been a sociable person, but we became quite reclusive," said Andrew.
"Everything felt geared towards children - even adverts on the TV - and so we began to feel completely alone."
Finding your tribe
For four years, the grief and depression overwhelmed them.
It was only by becoming involved in the annual World Childless Week, a global event to bring childfree people together, that Nicci and Andrew realised there were thousands of other people going through exactly the same feelings.
"It really helped us," said Nicci. "For the first time in years we're going around with smiles on her faces. We're members of a club none of us wanted to be part of, but it's a very supportive club."
It was this feeling which made them decide to launch their online subscription magazine for other child-free people.
It's just one of a number of ways childfree people are coming together to support each other.
Debbie Norman, aged 50, is a member of Gateway Women, an online community of childless women who meet up every month throughout the UK.
Before joining, she found it difficult to talk openly about the pain she felt at being childless.
"People would say: 'Why don't you just adopt?' They'd try and fix the problem or sweep it under the carpet. It just made me feel worse because my feelings weren't being validated."
The friendships she's made through Gateway Women have given her "permission" to work through her feelings and come to terms with her situation.
"It's not a life sentence," she said. "There is light at the end of the tunnel. It's not the future you planned but it's still light and beautiful. It can still be lovely."
The Institute of Public Policy Research estimates that, by 2030, there will be two million people aged over 65 without adult children, up from 1.2 million in 2012.
Approximately 230,000 of them will be in need of more than 20 hours' care a week and will have no informal support.
Ageing without Children, a campaign group founded by Kirsty Woodward for people over 50 who don't have children, is concerned about who will take on the caring responsibilities for childless people as they grow old.
A pilot scheme has been launched in Dorset which aims to challenge how services plan for people facing those circumstances.
Ms Woodward said: "Our care system still relies heavily on the younger generation caring for its parents - 95% of care is picked up by the family."
As for Nicci and Andrew, helping and connecting with other people means they can now look forward to the future.
"We've gone from rock bottom to feeling so optimistic and positive about the future," said Nicci.
"Helping other people has helped us heal. We've got a reason to get out of bed in the morning - which isn't simply to walk our three dogs."
Listen to Andrew and Nicci on the Stephen Nolan programme on BBC Radio 5 live on Saturday 13 January or afterwards on iPlayer Radio.