I weight 156 and am 5' 7". I want to gain at least 10 more pounds. I keep getting stronger, and look bigger, but I keep losing weight. I workout really hard, mixing it up a little. I take protein shakes after I workout, and I'm not sure what to do anymore.

Help?

You need to balance protein with carbohydrates and make sure you are getting enough vitamins and minerals. I suppose you could be malnourished, but I doubt it (unless you often feel fatigued or have been getting sick more often). Some people have high muscle density. When I was working out regularly, I would gain amazing strength (I could squat over 600lbs) but I never gained weight and only definition not size.