If you want clean mass, then apart from those supplements you should be eating more food. The mass gainer recipe suggested by @muskate is great. I have tried it, and loved it. The best thing about it, is that it is basically made of whole foods, unlike those mass gainers that you buy in the shop full of sugars and other shit that you don't need. After all, if you want to gain weight, let it be clean weight, and not just some fat.