Contrave side effects

So I’ve been on contrave for 3 days now and I’m doing fine only taking 1 pill so far til Saturday when I move up to 2 pills a day I’ve lost 7 pounds already I’m 5”9 and was 188.6 pounds when I started now I’m 182.6 pounds so the only thing I’m having issues with is at night when I go to bed my heart starts racing really bad but it’s weird cause it only does it when I try and go to bed at night I don’t ever experience it through out the day is this normal does it get better the more the medication gets into my system ? I am only on day 3