Bruises on Knee & Shin

Recently I noticed bruises appearing around the inside of my knee, lower quad and shin of my right leg only (also reoccurring). I know, for a fact, I did not have any external physical force hit the outside of my leg nor run into any objects...and I also noticed they seem to be appearing within 24 to 48 hours after running. I have been running 10-20 miles a week for over 5 years and never experience any issues prior.
No other present or past medical problems...3 months ago I have a physical with blood work which was normal...I maintain a healthy balanced diet (well...maybe a bit too much Dark Chocolate  containing adequate vitamin intake (especially B12, C & K)...from a layman’s view...could merely the physical stress of running continually break my capillaries...??
If anyone has input or past experience with this issue I was greatly appreciate your thoughts!! Thanks

Rachael