Hello ! I Am On Elmiron 100 Mg 3 X's

Hello ! I am on Elmiron 100 mg 3 X's a day ! Since then I have been having a very sick stomach , feels like i am going to throw up @ times ,gas , sore throat ! I feel terrible Also heartburn ! Urologist gave me them for very inflamed bladder due to a er rotted bladder mesh to smooth it out . He told me to cut back to two a day & I still have same results but my Dr. still wants me to stay on them ! I need to start feeling better ! i have tried OTC antacids & not helping ? What can I do to help my stomach issues ?