Thanks for writing in.
It could be a pilonidal cyst
. However , it would be best if you visited your doctor for an exact diagnosis.
In the meantime, you can apply some hot fomentation/ heat application to the area.
Is it the first time this has happened?
Maintain good posture. Sleep well. If you are lying on your back, keep a pillow under your knees. If you normally lie on your side, sleep with your hips and knees flexed and place a pillow between the thighs and knees.
Preferably dont sit on hard surfaces for long duration.
Keep the area clean and dry.
Hope this helps.
Dr. Divya Kuttikrishnan.