Trying to get pregnant

I am 24 and trying to get pregnant. My boyfriend and I have 1 daughter who is 2 years old. We have been trying to get pregnant for the past four months with no luck. My first pregnancy ended in miscarriage at 18 weeks, the doctors said there was no reason for it, it just happened. My second pregnancy was with my daughter. I did every thing as I was supposed to just as I did the first time around. Despite all I did to keep her in full term she was born at 34 weeks. I had early labor signs with her 3 weeks before I had her so the doctors gave me steroids for her lungs and different medications to slow my labor, but she decided she was ready to make her appearance. She had to stay in the NICU for 8 days to make sure she was stable and gaining weight. She is now 2 years old and at a perfect height and weight. So now we are trying to get pregnant again and it just doesn't seem to be working. I know these things take time and patience but I am just wondering is there any reason I should be worried about this pregnancy too, if it happens? And has anyone else had a similar story that could give advice? Thanks 💖