Your concerns are perfectly natural, just remember your stress is your babies stress though; you can only take care of yourself the best you can and hope for the best. I’m 21 weeks and will worry for the rest of my life now :X. It will be comforting when you get to see that baby for the first time [ I haven’t even had my first official ultrasound, only a peak at the ER 🙁 ]. Also, since technology is progressing so much, they’re able to see a lot of things they may point out to worry you (spots on the brain, kidneys, etc. that turn out completely okay!).
Just take care of your body, so you take care of baby.