What should a 4 month old weight?

My granddaughter look under weight. I am afraid she is not getting enough nutrition. She spits up half her formula and my daughter has tried several different formulas and acid reflux medicine and she still spits up her formula. The baby looks poorly and has bags under her eyes and she cries all the time and cries harder when her mother is not holding her. I think she should see a specialist something is wrong.