Hurt back of knee

Has anyone pulled muscles or tendons in back of knee and how long did it take to heal?
Around 5 weeks ago I was sorting out cupboards and emptying boxes which involved crouching low then standing up frequently. Next day the back of knee was extremely sore and still is. Standing from sitting hurts, I can only walk very slowly as it pulls and stairs are a challenge. I googled as you do and it's a common sports injury usually suffered by skiers to the back of the knee. I thought it was improving but yesterday after a short walk round a local nature reserve its as bad as ever. Any suggestions other than volterol which hasn't helped.?