Sorry you are having problems with this abscess. I cant give you too much advice about how something should feel after surgery as it varies person to person, so long as you follow up with your dr and surgeon to keep and eye out for proper healing and no infection.
You may be right in regards to recurrent abscesses due to fistulas, depending on how they drain them, sometimes they can tell if there is a fistula tract or not which is causing the abscess to reform later on. An MRI is a decent way to check for such things, if you were put under for the abscess surgery they should have been able to take alittle peek to see where the problem may be coming from, but with no clear direction and if the tract is quite small it may be difficult.
In my case I had an MRI that confirmed a fistula tract that ended up giving my a perianal abscess. I had a fistulectomy(sp) and the abscess drained with a draining seton put in. Pain was quite sore for the first couple days and tender to sit certain ways for a week or so. After 8 weeks I was working out and working full time again. The draining seton does not bother me and I run and do everything with it, but I avoid pools. I have had it in since oct 2012 and check in with the surgeon every three months. It is a big relief to not have the pain of the abscess. In time they told me the seton will be removed and everything should hopefully heal up.
I hope this answers some questions...
:) Take care