Hi Dustin - welcome! I'm so sorry you have to deal with a fissure when you're so young! Try not to worry too much, though. The surgery is really scary - of course, because it means cutting your butt!
but it really isn't too bad.
You should ask your doctor, but to try to answer your questions, I am assuming that you will be getting what's called a Lateral Internal Sphincterotomy (LIS). That means that the doctor will make a small cut on your internal sphincter muscle to stop the sphincter muscle from spasming and staying too tight. I know it sounds crazy, but it actually works very well. When the spincter is too tight and spasming, it blocks blood flow and that prevents the fissure from healing. When the sphincter is cut, it loosens and that allows blood to flow better which makes the fissure heal. That's the suregery I had and it worked very well. My fissure was healed in a little over two weeks.
I am also assuming that you will be having surgery under general anesthesia. The surgery itself usually only takes about 15 minutes to half an hour, but you'll likely be in the hospital for 3 to 5 hours, since you have to get ready for the surgery.
The pain isn't too bad. I'll admit that the first few days suck, but the pain is usually not as bad as fissure pain. The first poop is scary as hell, but it's usually not nearly as painful as people think it will be. You may have some packing up your bum after the surgery and that's uncomfortable, but it will come out and then you'll feel better.
Here are some tips: find a good stool softener. Many of us here find Miralax is very good to help make soft poos. The stool softener is important because you will be given pain meds and they cause constipation. Take the pain meds - your butt will be numb after the surgery and you might not think you need them, but the numbing wears off and then things get a bit painful. Just remember that you need to take stool softeners too. Seriously - stool softener! It will be your good friend!
The first few days are the most painful, but don't worry, for most of us, the pain after the surgery wasn't as bad as fissure pain, and the pain meds really help. Usually after the first three days, things start to improve quite a bit, but take it easy for at least two weeks.
There are lots of great people here who can give you really good advice, and we are here to support you. Ask any question you want. There is no such thing as TMI here!
Try not to be scared. Everything will go well, we are here for you, and you will be healed soon and the fissure will be a distant memory.