Ok, that still sounds like it may be some of the rollercoaster effect. If you need it every 4 hrs, take it that often* - that's why it's stated the way it is. As you heal, and the pain subsides, the need will decrease and you can back off the dosage. Most pain meds aren't affected by "taking with food", and that can help. If the upset stomach is intolerable, then I would still call the doctor and tell him/her and ask if there's something different you can take, or something you can take for the upset stomach.

Doc

*If it contains acetaminophen/tylenol/apap, do not exceed 1000 mg. of that within a 6 hr. window or 4000 mg. within any 24 hr. window. If taking it longer than 1 week, the 24 hr. limit should be no more than 3000 mg.