Baby lorelai is still small

I had my 31 week OB appointment yesterday and the doctor is still concerned because I haven't gained any weight in the 2 weeks since my last appointment. I eat a bunch and don't exercise except chasing my almost 2 year old around the house. I'm still measuring behind and have to see a physical therapist because my hip alignment is off and they said my pubic bone is seperating. Anyone have any suggestions on how to gain weight fast when you don't have any money?