I have noticed that sometimes when I ride my left knee will start to hurt really bad. It doesn't hurt too much when I am moving and actively riding but when we stop to take a break or if I take my feet out of the stirrups and straighten my knee it hurts. Sometimes this also happens when I am at work, it hurts to straighten it. If I keep it bent it is only a slight irritating pain but when I go to walk I have to kind of limp so that my knee doesn't straighten out all of the way or else it is pretty bad pain. It also happens randomly when I get out of bed and sometimes even starts to hurt while I am laying in bed.
Someone suggested that maybe the fluid that my knee is supposed to produce between my knee cap and my joint is not being produced properly and is therefore causing rubbing. I can't afford to go to the doctors especially because it only happens every so often. It will happen and then go on for a few days but then I won't notice it for a few weeks or more. It just depends.