Re:Carbs or protein
Your stomach getting bigger may not be fat gain....it might just be bloating from extra carbs....you'll need to analyse your results over a period of time to see if your gaining fat.
Ab exercises will not reduce your stomach size. They are a resistance based exercise and therefore use the anaerobic energy system which recruits carbohydrates as its energy source.
Including some CV in your programme will help reduce body fat levels as cardio is predominently the aerobic system which recruits fat & carbohydrate to burn in the presence of oxygen.
If you are "bulking" and increasing your calories, it can come from extra protein, carbs, fats and what most people choose - a combination of all three.
If you want to get specific....write out a typical day then the daily total of macronutrients (protein, carbs, fats) in grams.
Then you can make sure you're getting enough protein in accordance to your body weight etc.
A good idea is to post your "typical day" in the same Diet & nutrition forum and your stats, brief training overview and ask for people's opinion on where to adjust.
The more info you give the more they'll be able to help.