Welcome to the forum.
I know the point you're at and it's upsetting for sure.
I tried most regular meds, including prednisone which didn't help me at all, and like you, I couldn't tolerate the mesalamines.
When my doctor got me to the point of giving me a choice between 6mp/remicade or surgery, I balked and decided to find my own way.
In my experience, there are lots of alternatives to prednisone and imuran, and you could certainly do some research.
Did you know the slippery elm powder is nature's equivalent to the mesalamines?
Have you heard of LDN - low dose naltrexone?
Are you on any probiotics?
Dx - UC 09/2010.Tried various Mesalamine enemas/suppos/pills with Prednisone for several rounds without any help.SCD Diet of proteins,veggies,salads, fruits, & protein shakes w/almond milk, Liquid Minerals& Vitamins,Maca powder,L-Glutamine 15g, D-Ribose 5g,L-ArgEthylEster,chia seeds,VSL#3,K2,VIt. D3 100,000 IU every 10 days.Canasa suppos. as maintenance.Transdermal LDN put me remission!