Yes, it is entirely possible to have arthritis even with negative blood tests; this is often called seronegative arthritis. Your symptoms of severe knee pain and stiffness after resting are very real and point to active joint inflammation. While Ultracet (tramadol/acetaminophen) and Omnacortil (prednisolone) provide temporary relief, they primarily manage symptoms rather than the root cause. Please be reassured that this is common and manageable. I highly recommend consulting a rheumatologist, who can look at the whole picture, possibly suggest imaging like an ultrasound or MRI, and help find a safer, more effective long-term treatment plan for you.