Its normal some ppl gain & some lose weight your berly in the beginning of ur pregnancy you'll eventually gain weight towards the end
Its ok I lost close to 10kgs by the end of my first trimester but I put most of it back on its just because you are probably not eatting as much or as often and your being sick alot
It could be because you're throwing up so much which is normal
If you are sick because of morning sickness or cause you aren't or can't eat that would be why and its perfectly normal