Just had my 26 week check up and my

Baby was measuring in 24th percentile for weight, dr said was small weight wise, but has me coming back for recheck in 3 weeks to check growth. I’ve only gained 6 pounds entire pregnancy and dr mentioned that to me today but idk what else to do, I eat till I’m full, I eat what I want but I’m not gaining... she marked “insufficient maternal and fetal weight gain” on my reason for recheck.. if I force anymore food down my throat it would make me sick.. but honestly how accurate are the weight measurements?