This is probably a perianal hematoma, but there is also a chance that it could be a prolapsed hemorrhoid, so you should visit a doctor just to be sure. People sometimes confuse the two problems, and are therefore unable to treat themselves properly, as the treatment is different for each. In any case, even if it is only a hematoma, you will need a doctor to get rid of it.
A perianal hematoma is a pooling of blood in the tissue in the anal area as a result of a ruptured vein. This may sound serious, but it is a rather minor problem, and can be solved quite easily although, as mentioned, it requires a visit to the doctor. The problem does disappear on its own within a few days - a clot will form and will eventually disappear, but it may leave a skin tag. It is therefore better to have the hematoma removed by a doctor. If you visit a doctor immediately, the blood can be drained quite easily with a syringe; by now it is probably too late for that, but the doctor can still remove the clot by making a small incision.
If the problem is actually a prolapsed hemorrhoid, the treatment will be entirely different, and will depend on how serious it is and whether there are any complications.
answered by M W