I have l5s1 disc herniatian,ostearthritus in facet and hip joints.suddenly started getting sharp pain in coccxy whenever i try to sit down or stand up.can this be referred pain or something else?

In my experience the coccyx, the cartilage tip of the lower spine, when injured or inflamed causes prolonged tenderness. I don't think you're experiencing referred pain from the herniated disc or facet arthritis. Have you been biking often or for long distances? Any other ,even trivial, trauma? Tendons connect to the coccyx & tendonitis is a possibility. An orthopedic specialist can evaluate you.

You describe "coccydynia", or inflammation and tenderness over the coccyx, which usually is secondary to trauma. This localized pain can be managed by a donut-shaped cushion, and occasionally benefits from a steroid injection. See an orthopedist.