My left knee throbs when i sit on the bed and my knee is straight. it hurts on the inner part of the knee. can you help?

Get ortho eval: Sounds like the space beneath the kneecap is involved. X rays will show,this and an orthopoedic eval will,confirm if this is a common problem of chdromalasia patella, or something else. Treatment can consist of strengthening quadriceps muscle, topical and oral NSAIDS, or injections.

Varies: Multiple potential causes from things like chondromalacia, which is an early arthritis of the knee to more serious conditions like an underlying meniscal tear. I would not hesitate to be seen for an accurate diagnosis.