I'm in a similar position to you in as much as my body uses up the calories pretty quickly, i also struggle with eating loads of food too. Lately i've been using ultra fine scottish oats from myprotein, simply mix them up with a protein shake to get some extra complex carbohydrates into you diet. They're basically powdered oats but they mix quite well in water and are very cheap and convenient, especially for breakfast time when you dont always have time to stand in the kitchen and cook.

http://www.myprotein.co.uk/bulk-powd...scottish-oats/