What Causes Nausea And Dry Heaving While On Phenazopyridine?

I had an R TKR on 11/30 and have been doing great with pain meds, 5mg oxycodone 500 mg of Tylenol every 6-8 hours, on 12/24 at 3 am on got up to pee and had classic symptoms of a UTI, I was uncomfortable for 2 hours and then rested until I got up a 7 am. I went to local FastMeds Urgent care I was seen by a PA who has seen me before, she prescribed Nitrofurantoin 100mg and Pyridium 200mg (Pharmacist gave me the OTC equivalent Phenazopyridine HCI 97.5 mg 2 pills 3 times a day) I took antibiotic yesterday at 11:30 am and a dose of the Phenazopyridine. I took another dose of Phenazopyridine at 5:30 pm and again at 11:30 pm with the antibiotic, I woke up at 3 am and had a BM, then became nauseous and dry heaved. I did not take any more of the Phenazopyridine today, I did take another dose of the antibiotic at 11:30 am, I hadn t eaten much, tried to stay hydrated then at 5 pm I had diarrhea and dry heaved again, I was uncomfortable for 30 min. then rested. I don t have a fever, I don t have chill, no pain in lower back