My Baby Is 4.5 Months N She Is Nt Gaining

My baby is 4.5 months n she is nt gaining weight.. earlier she was taking lactogen as pedia advice v strt lactodex LBW to gain weight.. bt from few daays ger motion is very tight n she pressuring all the time n yesterday there was blood with her stool.. n she cried at hard.. it is very difficult situation.. stools was stuck in her rectile area n was nt coming out.. wqt to do.. her stomach is not good by digeation..