Can't gain weight. ..

dont do big weight if u wanna bulk up.... lots of pushups and squats are the way to go. dont start off doing a crazy amount when your first starting off, do a certain amount....stop... and then do that over ten times. and remember your muscles need time to rest or they will come back weaker

 

If you're 16, you can gain weight easily all by yourself.

Do squats, bench press, deadlift, row, pullup, dip.
Heavy weight, 5x5 reps except the deadlift which is 5x1, build up to that 1 rep max.

And eat well, good food, not empty calories.

 

can i just ask what is the advantage of gaining wieght???

 

start by eating a dozen eggs a day, 2-4 with yolks, and add in two cans of tuna a day on 2 seperate sandwiches( one can per sandwich) and you will see size, add in a 30g protein shake and a penut butter and jelly sandwich with alot of peanut butter too. I need to eat roughly 4 -5 thousand calories daily to grow.
take my word for it as i have when tdown from 298 lbs to 207 lbs in a year and then in 5 months up to 238 lbs staying close to as lean as i was at 207 lbs. all without gear(gear=roids).

throw in some junk food too, but sparringly though as it will throw fat on you. make sure you eat a big amount of protein before you sleep.

 

Do you take any kind of medicine? Check that.

 

if you want to put on muscle do heavy weights with low reps, if you want more muscular endurance do small weight with high reps.
but your also have to eat right.