Why i cant gain weight unlike my friends....?

I'd been taking protein shakes about 5 months and only gained 4 kilos? I doubled up my food intake for lunch and dinner and lots of lots of supper. I drink at least 2 liter of water a day which i pee-ed alot.. Lol. My body weight has been going up and down like roller coaster .. why?? I weighed 59 kilos 2 months ago and now i only weigh about 57.5 kilos. I did alot workout every week. Though , i can see less improvement on my body building which i'm quite upset. I usualy bench press at 130 pounds at 5 to 7 reps x 5 sets ( i increase the weigh every month ) . My maximum bench press weigh is 190 pounds but only 1 rep x3 sets ( at most ). i did alot other stuff like pull ups, squats, sit ups. By the way im 18 years old and im short ( 170cm) only.. I'd already tried supplements like ( Appeton , Horleys , NutraLife ) . None really pump my weight .. =( .. i dont wana waste anymore of my cash bcoz my friends dont even take protein shakes and they can gain 5 pounds a week. Life's just isn't fair.. =(