Not gaining weight

On my 16th week na pero hindi ako nag ggain ng weight. ? Same pa din yung weight ko since last check up ko. Makakasama ba yun s baby? 120bpm lng din un heartbeat ng baby ko, considered normal pa din naman daw sb ni ob pero sabi nya mas gusto nya marinig mas mabilis na heartbeat. Worried aq kasi may history aq ng miscarriage at 3months noon bigla n lang nwla heartbeat... d aq makatulog s pagaalala.?