Um, I don't know if this will help but...
I know BCP increase your risk for DVT (Deep Vein Thrombosis) or a blood clot that forms in the veins (usually in your legs). Using BCP & smoking is an even higher risk.
I'm not exactly sure of the mechanism, but because the risk for DVT, it seems to me that BCP would make your blood become thicker & hypercoaguable (more likely for the blood components to stick to each other). So, the fact that you're bruising so easily seems backwards, like your blood is becoming thinner versus thicker.
So, I don't think that this is really helping you, but I wanted to offer what I know. (thanks to nursing school!)
I'm sure you've gone over it about 1000 times, but just wanted to double check that you don't bruise just as easily when you're not on BCP.
Also, the fact that you're bruising simply by being on your knees is concerning. Do you have anemia or any blood issues? Also, that it only happens at the joints is interesting. I don't mean to scare you, but I'd maybe ask my doc about it, and possibly get him to run just a general panel of bloodwork...
Sorry to ramble....but I hope I was able to help a tiny bit...& good luck. Please let me know if anything comes of this, I'm curious.
take care
