I'm not very familiar with the substance you are using, but I would try some whey protein shakes. It's been a while since i've bought whey protein, but one brand I remember is designer whey. I used to get the vanilla flavor.

I have the same problem as you. However i'm 5'5 and weigh 113. I want to weigh 125-130. I recently got into the gym and doing exercises has increased my appetite. You could also try drinking oatmeal shakes. You take one glass of milk (soy milk is best because it contains more protein that normal milk), and add three or four tablespoons of oatmeal. Three tbs of sugar, some ice and an egg. Put it in the blender and that's it. I gained two pounds after two weeks..But then I got lazy and stopped drinking it.

Yesterday I bought this shake called "real protein" but since I barely started drinking it I can't really tell you the results. I'll let you know in a near future. Good luck with the weight gain, I know how frustrating it can be!