Little weight gain...

I’m just a couple days shy of 35 wks. So far I’ve only gained 5 lbs. From the beginning the Dr only wanted me to gain 15 lbs because I was already overweight ( Pre-pregnancy 235 lbs and I’m 5’7). I’m built like a man lol, I kinda have an athletic build. At first Drs seemed to be worried I wasn’t gaining weight but since Baby was growing they stopped questioning me about my eating habits. Anyways, has anyone else had trouble gaining weight? I’m terrified the baby will have a low birthweight despite what the ultrasound tech says...