Hiii doctor my age is 22 and my weight is about 50kg and i look weak i used multivitamins for months but it doesnt work?

Depends on the goal: In the U.S., people rarely "look weak" due from a reason solvable by taking multivitamins. Much of our food here is fortified with vitamins, so we don't see many problems of vitamin deficiency. That means the vitamins may be working just fine, and a person will "look just as weak" as before taking vitamins. It means that "looking weak" may have nothing to do with vitamins. A doctor can evaluate.