Buttock 

Buttock pain can be caused by inflammation of the tendons that are attached to the bone you sit on (the ischium). These tendons are together called the hamstring. The injury that causes the pain is called hamstring origin problem.

Symptoms may include aching or sharp pain in the upper hamstring or the buttock.  Pain when running, particularly at faster speeds, when sitting on hard surfaces and when driving.  Can also be painful when the hamstring is being stretched or being used to resist a force. Sometimes there can be aching, or less frequently sharp shooting pains into the hamstring itself.