I started out the same as you bro. I was weighing in at 118 @ 5'7 and thought I couldn't gain for shit. You really need to just pack in anything and everything and worry about the fat later on. Follow all the aforementioned advice and let your body get used to eating every 2 hours. As soon as that happens, you'll become more hungry and start to pack it on with ease. Also, if you happen to wake up in the middle of the night, go down to the fridge and eat some chicken w/ rice, or something to fill you up until breakfast. Make it a habit to wake up if you have to.

Good luck and keep us posted!