My 6 month old hasn't gained any weight since she was a mth old. doctor put her on juice& food 3x daily@ 4mth

also fed won't take formula was diagnosed wth failure to thrive. still no wait gain. doctor did blood work up/ evry fine other 2 children gained a pound a week third child i am worried had placenta previa first 5mths and shots to develop lungs at 7mths due to premature labor but baby was still born at 39 weeks 6ibs 11oz gained 4 1/2ibs 1st month now only gained 11oz she has grown 6 inchs now that she's eating and drinking 3xdaily now milk is drying up. she is 3rd to be fed others were very healthy. could i have bad milk. i don't like giving her so much juice 8oz daily. my husband & i are over weight juice is not good. can i switch her to goats milk or something ealse. the doctor has mentioned plagiocephaly but keeps measuring not sending to specialist. he says her head isn't getting bigger she's ok but could all this be tied she goes in 1x a week for check ups is not latharjick coplection,color are good, she has fat cheeks and fat rolls,eyes are bright loud cry. help