I hope I am not too late in advising this but never-ever go for weight gainers because not only they are ineffective in the long-term, they also harm the body badly, especially the kidneys. A lot of people have used weight gainers like Endura Mass upon rigorous advertisements and they got no benefits at all. These and many of those advised by the gym professionals are not too healthy for the body. You may get a good-looking body initially but the repercussions are severe and you would face troubles later in the life.
Instead, try natural weight-gaining products. Go for bananas, yogurts, peaches, plums, banana shakes, gram, moong, soybeans, peanuts, peanut butter, flaxseeds, chia seeds, eggs, and other such products that help you increase your weight naturally, Products such as Protinex could also be used to fulfill the daily requirement of proteins in the body. These products do not help you at once. Maybe it would take more than a year to help you. However, these are still better than unnatural proteins and weight gainers that harm the body.