Hey /fit/Skinny guy here. I've started eating a lot more once I started working out and so for it's going pretty well. Though now that school started, the cross country team started up too. I'm only about 120lbs~ and was wondering... if I'm running 7km 3 times a week.. is this going to be a problem for me? Should I stay away from that until I've put on more pounds, or will it not really change anything for me?
As long as you are consuming more calories than you are expending, then it won't be a problem. The problem is finding time and a healthy/balanced diet to gain weight.