Hello, For The Past 3 Days I Am Experiencing Pain

Hello, For the past 3 days I am experiencing pain on my left buttock. There is a small swelling in that area, and it hurts really bad. It pains even more when I sit. Though its size is not big. On the 1st day, it was little bigger and I could feel that it was hard. But today, it got broken on its own. At 1st when I wiped it with a tissue, I could see some orange colored substance. Then after while, it started bleeding.
Further information: Last day, I had a checkup done for runny nose and throat pain. And the doctor said me that I am having pharyngitis. At present I am taking medication for it.
I would like to know, what is the reason for the swelling? do I need to go for a checkup again? And what should I do to releive the pain? Thanks in advance.