I was a big headache sufferer before surgery and was also to be found snaffling lots of over the counter headache remedies but since pre op and surgery (12 weeks ish) I haven't had a single one! I am convinced my headaches were at least partly due to the huge amount of carbs and sugar that I was eating, slamming my blood sugar levels up and down. Sugar withdrawal was certainly the reason for my 4 day migraine at the start of the pre op diet but it's amazing how much better you feel even after those first few days of not eating rubbish.
I know you have a medical issue to deal with too but I wouldn't have thought lowering your calories, fat and sugar intake would exacerbate that!? My best advice would be to try and cut down on the carbs and sugar gradually ahead of the pre-op................I wish I had!
Best of luck with all the build up. I'm a sleever too so any q's, fire away and I'll try my best to help although there are much more experienced sleevers than me about too.