I'm a 22yr old pretty inactive female, why does my hip give me pain when I sit?

Impingement? Hip impingement or femoral acetabular impingement is a diagnosis that encompasses a bony or mechanical pinching at the periphery of the ball and socket hip joint. One of the common symptoms is pain while sitting because of the flexed position of the hip. You should see an orthopedic hip or sports medicine specialist trained in hip pathology to evaluate your specific condition.
Tendonitis. Could be as simple as sitter's bottom, which is a tendobursitis at the ischial tuberosity, the proximal attachment of the hamstrings. Hamstring stretching, anit-inflammatories, deep tissue massage, and a doughnut hole cushion to sit on are usually the mainstays of treatment. The pain is usually in the buttock region, or back side of hip.