I started at 114 lost 5 lbs because I cut out all the fast food. I started gaining around 20 weeks. Now I'm 32+3 and I've gained 27lbs! As long as your baby measures normal your fine. My nutritionist told me to add a serving(1/2 cup) of pasta or rice to one of my meals and drink an extra glass or two of milk.
I'm 19 w tomorrow and have lost 4 lbs. I lost 15 but gained 11 back.