Shin issues - strange bruising

So about a week ago my shins started bugging me. Only periodically and never during a workout. More when I woke up or just walking around the office after sitting for a while. It's continuing, but it's not constant and I can't pinpoint anything in particular (a pair of shoes, only after periods of immobility, etc) although the immobility does seem to exacerbate it. Normally once I'm up and walking for a minute it seems ok, other times they continue to hurt. Now for the really strange part. When I work out, my left shin errupts in bruises. I counted 6 distinct large blue bruises during my bike ride Saturday. After today's swim the entire shin was blue! If I push on the area where a large bruise was seen, it is slightly sore to touch even after it's gone. The other strange thing is the bruises disappear after an hour of being done with my workouts. I haven't gone to the doctor because I'm not sure what to tell him - "my shins randomly hurt and bruises appear after hard efforts but you can't see them now"? Has anyone experienced anything like this before? Any guesses on what it could be or advice? Anything is appreciated as I'm at a loss on this one.