Increased caloric intake, again assuming that the calories are from healthy foods—lean meats, fresh fruits and veggies, legumes, whole grains, and fresh dairy—, will assist you in gaining mass. I suspect what you characterized as "not eating a lot" may contribute to your difficulty increasing muscle mass. You don't
need supplements, you can gain muscle mass and such with a decent diet, but it's the high rate of protein in the powder that is a more efficient than just drinking milk and more palatable than having a lamb smoothie for breakfast.
