How to gain weight or gain more features?

I'm in my 20s, and from a family that are all genetically petite people. I know someone my size/stature but older than I am who seems to have a little more weight and a much larger um, chest. It makes me so self conscious and makes me feel worthless, really. I have some pudge on my belly, and was doing 1k crunches a day and several hours of cardio but its making my chest even smaller. I want to gain weight, and have even taken to getting the most fattening things on the menus at fast food and regular restaurants. I'm sick of being so small statured! My chest is honestly about a 34-36c but was a 34dd before I started working out and lost them. That's super small! I haven't been able to gain weight from my prescription Prednisone or the many, many (about 5-7 kinds) of herbs that I take for weight gain/breast growth. What foods should I look into? Should I buy a weight gainer at gnc? I never ate breakfast before, but have taken to doing that in order to make myself gain weight.