Anyone else suffered this?

What causes it?

Some information: I felt it come on about 24 weeks ago, it was only noticeable when carrying my bike upstairs after a long ride, but it progressed to the point where walking upstairs on my rest days was tougher. They'd start to ache 3/4 of the way up, then 1/2 the way up.

Then I got an injury (knee tendons), 19 weeks ago. I immediately rested, probably too much. No exercise until 2 weeks ago when I started short gentle rides around the block (the whole time I've been stretching and massaging). The heaviness and weakness has not let up though, sometimes I think It's getting worse. It's difficult to describe, kind of like a burning/aching within the muscles whenever I use them, quads, hams and calves, both sides. Now it's at the stage where even standing causes them to ache, and just one step of the stairs is tough. I've moved to a bedroom on the groundfloor so I don't have to use them so often.

If you have any ideas please share. This has been going on too long.

Thanks.