It doesn't work for everybody, but I never went cold turkey when I turned veg*n. I stopped eating red meat, then bird, then fish over a course of four months. Finally, cut out the fish because I didn't feel as if I wanted or needed it anymore. The rest of the stuff, like eggs and cheese, left on their own accord as well, though sometimes I eat them when I am visiting or for a treat. So, my advice would be, if your body can't handle it, it is probably because it is a sudden and shocking change, and the change keeps happening because you are going back and forth. I can't imagine going back to eating meat after going veg for a while is very good for your system, either.
If you really have cravings, try and eat some high quality mock meats than have plenty of protein -- I normally wouldn't recommend these because they have so much salt, it may help you in the long run.