I've been having knee pain for 3 years now and I'm only 22. Could it be early signs of arthritis?

Possibly. Although, the incidence of osteoarthritis (wear and tear arthritis) is negligible in people of your age, there are types of arthritis such as rheumatoid (less likely if your pain in the knee has been unchanged for 3 years and there is no swelling, redness/heat or other joint involvement). There are some infectious arthritides such as reiter's disease, but that's uncommon, too. See a doc!
Early arthritis. It's hard to answer your question without further medical evaluation. You should check with your primary care doctor and get a physical with x-rays and blood work. After that you can be referred to an orthopedist or rheumatologist depending on the results.