You might've tapered too quickly off of pred before the remicade had full time to respond. It's possible remicade did nothing and only the pred was holding you up. It's possible that you just got a GI bug/flu, especially with the quick onset and fever. It's possible you got c diff, and infection which your stool test should check for (c diff mirrors uc symptoms and only lab work can tell which it is). Lots of possibilities, lab tests and experimentation can determine which it is. I'd lean on your doctor there on which it is.
Rather then guess if you are failing remicade/infliximab or not, you can ask your doctor to order this test from whatever your local lab is:https://www.labcorp.com/test-menu/29496/infliximab-concentration-and-anti-infliximab-antibody
20% of us initially respond to remicade but have a waning response over time, and often an increase in dosage and/or frequency can bring them back into response again. The test checks for antibodies to remicade (which make it less effective and/or stop working entirely) and your current remicade-blood levels, which is helpful in dosing, some need more medicine than others do (variables disease severity, how quickly our blood clearances proteins like remicade from our circulatory system varies among individuals). Typically the test is taken within 24-hours before your next remicade infusion, when the concentration is at its very lowest.
That test isn't absolutely necessary, as your doctor can just experimentally increase your dosage and/or frequency and see if you improve or not. Remicade can be dosed at 5mgs per kilogram or 10 mgs per kilogram. Remicade infusions can be given every 8 weeks, 6 weeks or 4 weeks. You can ask your doctor if it makes sense to increase your dosage or decrease the frequency between your infusions, as it sounds like you had an initial response at least.
Generally they get you through the first 4 dosages of remicade to see if you get a response and determine success or failure based on some improvement within that timeframe. The odds are about
65% that you/I will respond to a remicade, unfortunately not 100%. A full remission from remicade might take multiple additional months, 6-months, or up to a year.
There are other medications to try, if your symptoms and condition warrant it. There's entyvio, xeljanz, and a couple sister meds to remicade (humira and simponi). In some cases we do have emergency surgeries, mostly when we do not respond to the steroids at all (IV solumedrol and pred tablets provide no relief, and they are worrying our intestine might perforate due to the severity of the inflammation; perforation = sepsis a body wide infection).