Worried about baby's weight

I'm worried my baby isn't growing correctly. My reasons are

1) I feel like my bump is too small for 27 weeks

2) all the way through my pregnancy I haven't had a good appetite, can't eat much

3) I haven't gained any weight since my very first appointment at 8 weeks

My midwife hasn't measured my bump yet or been checking my weight, so I'll mention this to her and let her know I'm worried. But I'm just wondering if me not gaining weight will cause my baby not to gain any weight?