I agree with the above. If you are looking to put on weight, you need to do it through proper diet and training.
I was in pretty much the same boat you are. I was 6'0" and weighed ~145 pounds, and no matter how much bad/junk food I ate I never put on a pound. Eventually I started eating better and working out, and I managed to put on 15 pounds in the course of two-three months.
Unfortunately, my weight is again frozen, but still that 15 pounds makes me look and feel a lot healthier.
I still occasionally splurge, though, just because I can.
