Try Cortifoam made by Schwarz Pharma - it has been my life saver. I too tried rowasa, but I felt like my butt was going to explode with the pressure - I could never keep it in past a few minutes.
Canasa is easy to keep in, but too mild, and didn't have any immediate relief.
After Cortifoam, within just 2 applications I knew this was going to work. My throbbing ended and next day was able to minimize my time I spent in the bathroom.
Cortifoam is a local steroid, with minimal side effects if any. I have been on it for a few months and haven't had any side effects.