Ugh I need advice

I've never been the type to thing negatively on anything! But my whole pregnancy has been a struggle with not being able to see or hear my babies heartbeat for weeks at a time. I'm currently 15 weeks therefor I haven't felt my baby move at all, my last appointment was at the 13 week mark and my babies heartbeat was good and strong. I won't be seeing my baby until I'm about 18 weeks and I cant help but stress thinking "is my baby still alive?" "Will my baby be healthy when it's born?"