Presacral collection and abscess are pretty much the same thing. With the abscess, there is more of an indication that there is infection present.
This has nothing to do with your stoma antics. More likely, it is due to your internal bleeding. After it clots, it liqufies and settles where gravity takes it. The presacral space is a common site. This is the virtual space between your low back (sacrum) and your rectum (or j-pouch in your case).
Blood collections that become seromas or abscesses can become infected if they do not absorb in a reasonable amount of time. That is why they like to drain them.
I had a presacral abscess that held about a pint of fluid. I only had low grade fevers of 100 or less for about a month, then BANG! I had a fever of 105. I had to have a drain in for a month. But I did have other symptoms before the fever, like a lot of pain.