Well without clinical examination exact assessment is not possible but your symptoms needs a surgical consultation to rule out an underlying sinus tract.When a pilonidal sinus becomes infected, it can be sore, red and swollen.Well depending if there is a tract inside than a surgical procedure.
Wide excision - removing the skin from wide area around the sinus, and allowing it to heal without stitches. This method takes some time to heal, and dressings need to be changed regularly, but it means there's a low chance of the infection coming back .The time of healing depends upon the lenght of tract but more than two weeks at least.This is not a emergency operation. For immediate relief you can soak the area in warm water and take painkillers such as ibuprofen(Motrin 200mg SOS), which will also help ease the swelling. If you have a lot of hair in this area, remove some of the excess.
My point is it is better to rule out the possibility of sinus tract there before self treatment.
Check this link
http://www.nhsdirect.nhs.uk/articles/article.aspx?articleId=285§ionId=1180
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