I had a presacral abscess/collection after my step one. I didn't seem to have a fever, though I had night sweats. Maybe the constant paracetamol I was on kept the fever down!? Don't know.
I felt shocking though. Extremely lethargic, couldn't sit up for lack of energy. I thought it was just a normal part of recovery (it was my first colectomy, lol). It was eventually diagnosed and a drain put in a few weeks after step one.
There was some talk it was caused by a blood clot or a leak at the anastamosis. Thankfully, my scan before takedown showed no leak, and I was reconnected on schedule. And *touch wood* I have had no further issue.
Hopefully it is a good sign that you have been feeling well, and it can be dealt with simply.