I'm no qualified nutritionist or PT but I have been doing this for a long time (ex GB athlete) it sounds to me you are abit more carb sensitive or have a lot of carbs? Maybe something you want to focus on.
Really cut down on the pints. No alcohol is good alcohol but atleast switch to a spirit with a diet coke or tonic rather than pints which are just shy of 200cals each.
Its well worth splashing out abit of money on an experienced trainer with a good reputation if you're really serious.