Do you feel like something is wrong? I'm 24 weeks and haven't seen a doctor, I'm looking for a midwife but I will be refusing to have an ultrasound unless there's good reason to believe that something may be wrong and I can be recommended to a specialist. Anyway I'm small, I haven't gained much weight but I listen to what my body tells and I feel my baby is growing as he should and is doing just fine, I haven't experienced any complications thus far. Every women's body is different, and being "too big" or "too small" doesn't mean something is wrong, only if feel like something isn't right. In pregnancy our bodies are designed to accommodate the needs of the baby, this includes weight and size, you the form you do while pregnant because it is what your body believes will help you to carry and give birth to the baby.

I think you can go to the doctors and say your not feeling well and they will do an ultrasound and while they are you can ask how she is doing.