Like everyone else is saying...Eat more! 5oz steak???
2 quick tips:
Tuna is fine, but add more meat! Buy lean ground beef, make up a pile of chili, freeze some so it's always available.
Add peanut butter to your shakes (lot's of calories).
There are a hundred ways to add calories, think of some by looking through the articles (Dave Barr wrote a Bulking Tips article). Remember this, you're fairly young and you likely have a relatively fast metabolism, so if your not constantly eating you will not add much mass.
As far ar the training you need to add in some more back work (esp. rows). Train either way, body part splits or full- body, they'll both work if you put in the effort. But if you do full body, set it up so the large muscle groups are first and move abs to the bottom of the list.