A hematoma, on any part of the body, is an indication that there was a flow of blood into the area due to a blood vessel bursting. In other words, it is a bruise. Normally, there would be a certain level of swelling in the perianal region because of the accumulation of blood but the swelling that you have described seems to indicate that something else might have happened. You should get yourself checked for an infection. The perianal region is highly susceptible to infections after a perianal hematoma due to the presence of fecal bacteria. The most likely cure that your doctor would prescribe is an antibiotic that could be an ointment or an oral dose.
In the meantime, you should not stress the tissues around the area too much and try to shift to a completely liquid diet. Some of the dietary changes that you should consider for the next few days, while your condition heals are an increased carbohydrate intake. Remember to reduce fibrous food, as this is mostly un-digestible material and would end up in your stool. A high intake of dairy products would also be of great help. Physically, it looks as if some kind of a papule has developed in your perianus so do not try to place any pressure on it. When you have to sit, try to sit in a position that does not put any pressure onto your anal region or use cushions for the next few days.
A hematoma will usually heal over the course of a few days and is not a medical emergency unless badly infected. The body heals a hematoma by reabsorbing all the blood that has been lost to the surrounding tissue. There is however, a way in which you can speed up the healing of the hematoma and that is by resting completely for a period of a week – preferably in bed as well. While you are lying down, try to place a few pillows under your back in such a way that your buttocks are at a higher level than your heart. This will start a drain of blood from the area. Placing ice packs on the area will also help prevent further bleeding into the tissues by constricting the vessels that are bleeding into the area. The point of rectal hygiene cannot be stressed enough at this point. You should use antiseptic soaps and keep the area dry during this time to avoid any kind of bacterial infection.