Try this link, might just help.
http://www.bodybuilding.com/content/skinny-guys-guide-to-gaining-weight.html
Weightlifting helped me a lot with a good balanced diet. I was 45kg and now I'm 55 kg just after 3 months. Never took any supplement just a lot of protein intake.
You could also for a few calories add cuppa soup each meal especially during winter months
Try and eat atleast 600-700 calories per meal around 3,000 calls a day . Dense food that are low glycemic . Peanut butter , chicken , oats & sweet potatoes , eggs , steak . Stick with the basic compound exercises 3 days a week and drink a lot of milk and try to sleep at least 8-10 hours a night .