Hi Paula,
My advice would be either to see a doctor or a nutritialist. Things don't seem to be going right in your body. Naturally it is hard for our bodies to accept change when it has been conditioned to eat the same things for long period of time. It's good to hear that you are going at this slowly, so you'd think after a couple months your body would have adjusted but since its not, you should definatly try to get some real medical advice.
I havent really experienced this myself...right before i slowed down my purging I had the opposite problem with having to go to the washroom a lot, and now its stopped I still find myself having to run there every day. Eating disorders are definatly not good for the stomache.
But keep at your recovery, feel proud that you are overcomming the monster, and good luck!!