I need your advice so much.

I had my first baby last year but unfortunately she had a heart problems and the doctor told us that she needed a surgery, so she had a surgery bur she couldn’t survive. I was so depressed that time. I was scared to get pregnant again, because I thought that I would face the same problems. So me and my husband went to the doctor did all the tests to prevent anything like that in future. It took me a year to find out that we are able to have a healthy baby. Though nothing was wrong with us. nobody could tell what caused baby’s heart disease . All this time we had protected sex and finally when I decided to get pregnant again my periods got mixed. I always had periods on time. Last time I even thought I was pregnant. but when I got my period 5 days earlier I got so depressed again and I had pain in my stomach and back( which I never had before).My doctor says that nothing is wrong with me and I shouldn’t be obsessed with pregnancy that much. It’s easy to say but hard to do. I hope you understand me.
I wonder is anything wrong with me again? Why can’t I get pregnant? I wanna have a baby so much(
Please if you have any comments let me know. do I have to do the check up again? has anybody faced the same problem?
I am so looking forward to your answer.