What Hopper said. Gaining size at the point should be pretty easy. Even if your training wasn't working, if you were eating enough the scale would still be moving up (fat gain).

Weigh yourself once a week. If you're not gaining 1-2 lbs per week, eat more. If you're gaining more than 2 lbs per week, back off a little and see how you go. This should be fine for 6-12 weeks or so.

Good protien sources are
Any fish
Any lean meat
Any poultry
Eggs
Cottage Cheese
Quark (if you have it in your area)
Milk

Good complex carb sources are
Brown rice
Brown pasta
Brown bred
Potatoes
Crackers of various sorts

Good simple carb sources are
Any fruit (bananas are a popular portable choice, but eat a variety of fruits)
Any fruit juice


Eat protien all day. Eat more simple carbs after training and complex carbs during the rest of the day. Take it easy on carbs in the evening. Don't forget your vegetables! They don't have much caloric value, but have plenty of vitamines that eveyone needs.

Learn how to read a food lable and weigh food. This is very important. You can't know how much you're eating it you don't know how to value and measure it. An easy way for you to start out at this point is to eat about 3000 cals a day and adjust based on what happens each week. You may think that's not much, but 3000 cals of good food (no big macs and doritos) is actually quite a bit for a smaller guy who's never done it.

Good luck mate,
Jeff