I also have had many headaches, and at times just behind the left eye. I went to the optometrist, in a way, I thought he would say there's something wrong with my eyes other then that I'm short sighted. There isn't, but I'm on prednisone, and this can cause pressure apparently. I think most the headaches, besides it being one of the major side effects of prednisone, is candida, in part dehydration, then sometimes if Iv had less sugar, and sometimes low blood pressure. But prednisone can cause probs on it's own, and eye problems are common in crohns.