Please put weights and a timeline on that description...
the short answer is... eat food. Seriously. I've gained 60lbs since I started. It takes HARD training in the kitchen. Eat beef, lots of it, and drink milk. Find a burger recipe that makes your mouth water and eat burgers a few times/wk.
Are you full right now? If the answer is "no" go eat food. After that and every 30 minutes thereafter for the rest of your skinny life ask yourself that question. If you are not uncomfortably full, go eat food. This is how I went from 148 to 208.