What is this?

So for the past few months my left leg has been hurting below the knees making it painful to walk. It mostly happens when I get off the bus and am walking home but as soon as I get home, it stops. One time it was hurting on/off while I was out and again when I got off the bus and was walking to get home. When I'm at home I never get any pain, if I'm standing for too long then it may be a little uncomfortable but no pain. I'm thinking it's some kind of injury as I'm always bumping into things in my as it's so small that there is barely any space to move or it could be because I'm mostly at home and rarely go out but I don't get why it's taking so long to heal. I did some research and apparently walking helps. I've been walking on the spot at home whenever I can and remember and I think it has helped because the last time I went out and got the pain while I was walking to get home, the pain was slightly less still painful but it wasn't as hard to walk, previously I had to walk as slow as possible and straighten my leg as much as I could to make it less painful but the last time I didn't have to do that. Any idea what it is or anything else I can do? Would stretching help?