Not having enough feeding and not sits.

Hi All, My baby daughter is 6+months old. Ever since her birth, we had to feed her with mother milk and lactogen formula milk due to insufficient mother's milk.  From last one month she is not  allowing us to feed lactogen formula milk and not sleeping enough. She responds well with vision and sounds. But she can't play on her own and always needs one assist. But neighbour kids of her age are playing on  thier own. She not properly sitting and crawling. Other neighbour hood kids of her age are very calm and playing enough. When she cries she makes lot of noise and cries a lot. Is this considerably issue with our daughter's physical and mental health. If yes to which specialist we need to consult. I sincerely request to advise to make our lives better. My wife and in-laws lost their health dealing with our daughter. Thanks Srisaran S A