Headache/Lack of Sugar & Caffeine

I'm currently doing the Soup, Salad, Sandwich diet (2 weeks prior to surgery). I've completely cut out all juices, soda, and powerades from my diet. I generally drink about 3 powerades a day plus various juices once I get home from work (never been much of a soda drinker). I've noticed that since I've started this diet I've been getting pounding headaches by the end of the day. Could it be from the lack of sugar/caffeine? My energy level isn't great but I wouldn't say it was drastically different from before the new diet. Any ideas? I'm thinking it's mostly just my body trying to adjust.

I have just finished this part and started the clear liquids. I too had severe headaches within 3 days of starting that diet. I took 2 tylenol and it got better but never went away completely. Funny thing is I don't have it now and hadn't thought of it, so I don't know when it did go away. Use the tylenol it did help me alot.