Quit eating the fast food. Start buying pre-packaged healthy options that are now available to you in any grocery store. Mass is only accomplished by repetition of eating protein, consistent workouts that are heavy....heavy!
If you don't eat enough food with a high amount of protein, your going to burn through calories that you take in, and not allow your body to grow. You can workout hard and not grow, and that is why people get frustrated and quit after not seeing the results they think they should see. Supplements are an illusion for you right now, don't rely on them.
You need to start with a nutrition based mindset and a workout that involves compound heavy weight lifting to go with your cardio. Cardio will strip your size, not a bad thing if you like your current size. High cardio with a junk food diet means your cancelling each other out. The benefit is in that your making your lungs and overall stamina stronger. To gain anymore size, you need to do some research on different web sites on eating correct food for increasing healthy weight.
It is really simple, eat the right foods, and lift heavy weights, and you will grow.
"Kid, I've sat on the department ****ter longer than you've been a cop." (CatDoc to Chevy SS, the single greatest post ever on RP!)
Moon Pies and RC Cola make me happy