如何在沒有吃垃圾食品情況下增重?

和大多數人相反，我好想增重。I was used to be 110 pounds, now only 104-105 pounds. My dress size is from size 4 down to size 2 (http://bbs.wenxuecity.com/style/2090560.html). Is there any way I can increase my body weight without eating those junk food? I eat 3 main meals and 3 -4 times snacks, but still not gain any weight.