Everyone gains at a different rate and considering your gaining you should be happy, their is always going to be freaks. I helped train a guy that just looked at weights and grew he ran a couple times a week ate 4 meals a day, not enough protein and tons of carbs along with tons of ice cream and he was a shredded 240lbs naturally, i was like WTF!? lol Normally people call themselves a hard gainer after not being able to put on weight, and it really 9 times out of 10 comes down to not eating enough calories. If your metabolism is SUPER fast then you need to eat ALOT more then the average guy. I remember reading in muscular developement about an amateur named Jimmy Canyon and he was a shredded 170lbs yearound i believe but he had to eat 500g's+ of protein daily otherwise he shrank. I have buddies like these, they stop going to the gym and just lose it all in weeks.