I'm 19+4 and haven't gained any weight. My baby is growing just fine. Only be concerned if your doctor is concerned. My doctor isn't concerned about mine.
No reason to be concerned if your Dr isnt, for me iv only gained 8 pound im 22 weeks and I was always worried because I didn't feel the baby move but my Dr said the reason that I don't really feel baby move is because my placenta is in the front and acts like a cushion