+1. I'm assuming you're attempting to push a big gear too fast, too soon. I know you said you've been training this way for a few months; if that's the case and it's got progressively worse without changing anything to do with the bike, either your setup needs adjustment or you've got a medical situation going on. I'd fine tune the setup of the bike to best match your height/legs, take your routine back a few notches; if it doesn't improve, I'd see a doc.