Hi I have IUD for about 4 month now and recently I started gaining weight and my stomach looks like a baby bump but I have no symptoms of being pregnant what's so ever. I feel like my stomach is bloated. I have not taking pregnancy test, and sometimes I feel nausea. I have been smoking and drinking If I'am pregnant could it effect my baby?

Yes, it could. Best to find out whether you are pregnant. Either try a home pregnancy test or see your doctor.