Hi Canlafre
Yes, it sure sounds like you have a fissure. As to whether the seton placement is causing / has caused the pain, that could depend on what kind of seton you have. A fissure will no doubt result in pain, especially after a bowel movement, but a seton could add to that pain. Generally, setons are rather uncomfortable contraptions. I am presently on my third draining seton (I had an anal fissure, which led to an abscess, which in turn led to me having a complex fistula), my first seton was too loose and fell out, my second was too tight and I literally couldn't walk and was taking morphine for the pain, which felt like cheese wire cutting through my butt cheek (eventually I got an emergency appointment and my surgeon loosened it for me, but it eventually came undone and fell out). My third seton is still in and seems to be working ok but does give me much discomfort (not to mention the horrible smell). However, a draining seton is quite different to a cutting seton, which would typically result in far greater pain.
As someone else mentioned, the nitroglycerin paste that is used to treat fissures can result in really bad headaches, as it did for me. With my first fissure I had to stop taking it due to the extent of these headaches (I literally couldn't function and the headaches were simply too much to bear). When I developed a second fissure I flatly refused to use the paste again.
A Sitz bath is a great idea and is very beneficial in keeping the area clean following a bowel movement. I would certainly recommend purchasing one. As already mentioned by someone else, a hot water bottle is also a great addition in offering some pain relief.
I really hope you manage to find some relief and I hope that your problems are soon solved. Take care.
Martin