Dear Doc, I Do Have A Constant Pain In Both

Dear Doc, I do have a constant pain in both of legs (below and above knee) for the last more than two years. I feel very tired all day, although it does not occur while sleeping. Even when I get up in the morning, I feel very tired. I just want to take rest all the time. Its difficult for me even stand for more than 10 minutes and walk for more than 30 min. I feel my legs are weak and not able to take my body's weight. Could you please suggest me a line of investigation. Thank you very much.