Im severly underweight im about 5 11 120 pounds ?

i drink cyto gainer and muscle milk along with alot of water i eat 3 decent sized meals a day and i lift weights wen i get a chance. and i still dont seem to gain anything. wen i was young i use to play alot of sports and i was told i built up a very high metabolism which is why im so skinny any suggestions on what i should do?