it sounds like you're wheat-intolerant - i know feeling sleepy after wheat is a symptom of that. avoid wheat pasta and bread, and try other starch alternatives such as potatoes, oats and rice
the idea about eating small meals is a good one - there's no way you can get all your nutrients on 600 cals, it's just not healthy. build up to a sensible level of calories, 1200 as a minimum (even if this makes you feel full) by eating nutrient dense foods such as nuts, seeds, dried fruit, full fat yogurt...
vegetables and fruits are also important but don't over-do these if it means you don't have room for anything else.
how long have you been like this?
have you considered the reasons behind it?