Ihave very sever pain in my knee since 4years ago. My dr said its arthritis but im pnly30! .Is it true?

See your doctor. You could have a host of issues that could cause your knee pain, could be bursitis, tendonitis, arthritis, ligament issues, meniscal injury, sciatica etc. So you may want to see an orthopedic pain specialist that can tell you what is going and help you with the latest treatments or exercise therapies available. You may want to consider stem cell therapy as well. Regenexx.Com.
Maybe so. If your doctor made the diagnosis of arthritis based on your history, his thorough examination, and appropriate diagnostic testing, then most likely he is correct. A diagnosis of arthritis cannot be made simply because your knees hurt. Remember that arthritis is inflammation of the joint and may be present for some time before it causes discernible changes on radiographs of the knees.
Could be. Osteoarthritis, or inflammation in the joints, can certainly start at young ages, especially in people who have had injury or repetitive motion to those joints. It is usually diagnosed by history, examination, and sometimes x-rays. Other things that could cause knee pain include meniscus tears, ligament tears, or bursitis (inflammation of the sac lining the joint).