Aw OP I can relate, I felt exactly the same at your age. First there were non stop hens, weddings, engagement parties, then all the christenings, kiddie birthday parties. I am a naturally happy person who kept being happy for people and assuming my time would come. Then one day I wasn't happy or sure. I was just blue.
This coincided with me getting sick and being told I could probably never have kids. I was out for brunch with my two besties who both announced their second pregnancies. We talked of nothing else. In fact they were my conversations everywhere I realised - other people's news. And because everyone was retreating more into their family units I wasn't even really being included in plans so much anymore.
It dawned on me that I was left out. I genuinely through nobody else's fault WAS left out. I decided there and then I wouldn't feel obligated to go to kiddie gatherings or things that were going to make me sad. I knew my friends would understand if I explained. I only went to things if I wanted to (new experience for me). And I began doing lots of other things and got fussy about who I spent my time with (much more with single people).
I do know what you're saying about wanting to be with your own gang of good friends but those friendships won't die just because you do some stuff without them.
The other huge part of it is accepting your circumstances exactly as they are, right now. Everything changes for everyone all the time so all you can do is experience the current time. Yes it would be lovely to have shared pregnancies with your close friends but that hasn't happened. Accept it. Accept that nobody knows what the future holds.
I agree with the previous poster who talked about positive affirmations. Quite a lot of people think they are rubbish but I've always believed except for those few years where I began to panic and upsettingly I lost sight of what I wanted, my belief in myself and my own standards. In short, I became desperate and that is not attractive.
Anyway once I accepted the current situation it was massively liberating. I thought "well I have nobody to answer to but myself" and began filling my free time up with loads of cool things. I became really happy, fit, felt more attractive than ever and realised it was ludicrous to think I would not meet someone. I didn't know when I would meet him but I was happy with my life and if he came later and I never had a wedding or kids then so what. I knew inwasnt going to settle for any guy who didn't make me super happy either.
I really really became happy on my own. And then of course like all the cliches - I met someone. It's the best relationship I've ever had. I think if I'd met him earlier we would not have had the relationship we do. I had to figure out what I was looking for. We have a beautiful baby girl too. There is a definite upside to having a child after your friends - you don't buy anything and your baby is a novelty.
Keep the faith and be happy. Its also an emotional time of year.
Sorry this was very longwinded!