Hope they pass for you chick, I'm dreading it.
I remember when I was pregnant with my first, I craved full fat coke (no wonder I put on 6stone!!!), drank loads of it. When I suddenly switched to water because my gyno was worried about my weight I got massive migraines, I thought it was the water but soon realised it was caffine withdrawl and sugar withdrawl. Switched to diet or caffinee free and felt loads better.
I rarely drink fizzy drinks now, I try and drink more water which I find really helps with headaches.