Try Lyrical if it is fibromyalgia. Dr. prescribed
are you eating when you take them- i would try to eat something before you take the med that might help
You were used to being on a lower dose. It's probably nausea or something of the sort, yes? Take it with food, then lie down about 30 minutes after you take it. It'll help a lot.
If its a more intense "sick" You might want to talk to your doctor about it. Possibly prescribing nausea medications?
As for the Why. you went up on the main ingredient of the medicine. and went down on the tylenol part of it. Its a stronger medication. If you arent used to strong narcotics they tend to make you feel a bit nauseaus, tired, yucky in general.
It usually passes after you get more used to the drug though. As your tolerance to narcotics raise, so will your tolerance to the symptoms.
I think you'll be fine if you wait it out a little bit. Especially if you took the 7.5-500's with no issue. Your body is simply readjusting. You can always talk to your pharmacist about your symptoms and see what they think you should do about them :)