Morbid question

I'm completely paranoia something will go wrong in this pregnancy after 3 miscarriages, also read so much about late miscarriages and still birth (which hasn't helped the anxiety). I'm currently 16+4 and I like to know every possible bit of info I can.

So my question is, how would I know something has went wrong and what would happen next? My other question is, what's the earliest you can give birth and your baby has a chance?

So sorry if this is too much for some people, I'm just super anxious and if I can prevent anything by knowing the warning signs early then I will.