I think you should try to hit this hard. You could get mesalamine and steroid foam enemas. Use the foam in the morning after you're emptied and the mesalamine before bed or vice versa. I don't really like using a liquid enema during the day but that's just a personal preference. I've done it without any problem.
I think you should try another 5ASA if you don't see any results with Apriso. Not everyone does well on the same mesalamine medication and the dose of Apriso is lower than Lialda or Asacol, you may do better at the max dose, 4800mg.
Can you get tablets for the thrush? It sounds like you could use an oral rinse and possibly some Diflucan for a few days to wipe that out. That's one thing you should be able to erradicate. Prednisone does make you more prone to yeast unfortunately. I would recommend seeing if your doctor will give you a scipt for a few tablets of Diflucan in case you get more yeast.
I also think perhaps you should give the probiotics a rest and stay at 40mg a little longer if you're still having severe syptoms. Have you seen improvement at all? Is this your first time on prednisone? Prednisone nipped my flare quickly the first time I took it but the 2nd time on 40mg, it took 10 days and it was a slow taper with a lot of ups and downs. Finally I had to start an immunosupressant to get off without a relapse. I am not saying this will be the case for you, as it sounds like you haven't tried any of the traditional medications & there is a lot of hope for a less invasive treatment path but definitely try more medications if you're not seeing improvement with what you're doing.
One more question: When did you start Apriso? Some people don't tolerate mesalamine well and they high increased symptoms from the meselamine. When I was on prednisone, I didn't take any of my other medications until I tapered down and needed them and I was 100% symptom free.