@bloomety similar to you I had 2 MC after 3 years TTC and it feels like I have been trying to get PG, having tests, having scans, being PG, grieving lost babies while coming off hormones forever. It's a lot. And it really knocks your confidence.
Congratulations on your 12 week scan. I mean that. It's fantastic that it went well! I cried at mine as well - so shocked that it was alive in there. I also haven't told people other than my Mum and a close friend who supported my through my 2nd MC. I'm waiting until after the 20 week scan to tell other people. Halfway just feels less like tempting fate to me but it might be different for you. It definitely makes it more lonely with no-one to talk to so honestly I don't know if it's the right decision or not.
I don't have the answer I'm afraid. I'm 18 weeks now and I still struggle to get excited and continually worry. Things I am doing that help a bit:
1 - I am having counselling. I was properly broken after the 2nd MC (we'd seen HB at 8 weeks) and couldn't really function. I've kept the counselling going so I have someone to tell all my thoughts to! I'm lucky I can afford to do it but it's really useful to unpick the craziness.
2 - Counting in weeks. I haven't even thought past the 20 week scan. I've been really open with my midwife about how I feel and why and she lets me go to see her more often. At 16 weeks she let me hear my baby's heartbeat and then again at 18 weeks. 2 week blocks give me more manageable dates to work toward. I have another appt at 22 weeks, 2 weeks after 20 week scan. It took me ages to convince myself that this isn't just me being frivolous and using up NHS resources. I actually need this to cope.
3 - Distractions. Walks. Cooking. Music. Video games. Anything that gives me 10 minutes out of my own head.
4 - Hope. I actually wrote down "It is OK to have hope" in marker pen at one point! I'm still working on it but try to remember that having hope (or not) will not change anything at all and let myself have good moments and enjoy them.
5 - Talking to DH. He's way more excited than me and I need to see that! As soon as I start to worry I have to tell him so he can tell me I'm not being rational and it doesn't become a big thing in my head. This is pretty much daily... He's a saint. He really is!
I don't know if any of that helps but know that you aren't alone! You're doing everything you can for your little one - you're worried because you care about them so much and that's understandable and means you will step up when you need to. Try not to judge yourself harshly and hopefully it will get easier with time. That's what I'm hoping anyway! Sorry - long message!