I'm in the same boat as you, but I'm a bit older - 45 and single for the last seven years. I did have the whole - no husband no kids - crisis, and occasionally still do, but it was a chance visit to my GP for a minor gynae procedure that changed the way I look at things. She'd asked how things were in general, and I got upset and the whole no husband no kids thing all came out. She didn't skirt around the fact that it might never happen, but said, "there's more than one path in life to take to be happy". E.g. Just because it might never happen doesn't mean I have to sit in a pit of dispair for the rest of my life.
So, I did what a lot of other posters have suggested - I booked a holiday with Explore, around Greece on a boat for a week. I think I was 28. I was so terrified that I cried in the Macdonalds at Heathrow. Nevertheless, I got on the plane, and got to Greece, only to find that my luggage hadn't landed with me. The other 17 clients on the trip lent me everything I needed, and it really broke the ice. That trip was fairly female-heavy, but I had a great time.
Since then, I have booked other trips, but with Exodus, who have a trip loyalty scheme. I started with a cycling trip through the Atlas Mountains, then a cycling trip to see the TdF. The Delhi to Kathmandu trip followed - I did this over Xmas and NY as I have no parents and struggle during this period - then another cycling trip to France, one to Jordan, and one to Cuba. I am a cycling nerd but they do plenty of general sightseeing ones. Last Xmas and NY I trekked to Everest Base Camp, which blew my mind.
As I've got older I've realised that it wasn't just not having a husband and family that bothered me, it was also that everyone else I knew did, and women, mums, couples, family pressure etc, can really make you feel left out and isolated. Meeting such a wide range of people on these trips has made me realise that there are plenty more people like me, and they all give tips and advice on how to handle it when you feel down. I'm now going on my first independent trip completely on my own - no group - just a few days in Crete in October, and although I'm nervous, it's only for four days, I can read and sit on the beach or on the terrace of the little hotel I am staying in, and if I hate it, it's not long before my flight home. Plus, all my friends kids, especially the girls, think I am this amazing, itchy-footed wanderlust crazy godmother. One said she "wants to do what Auntie Chockaholic does" when she grows up.