Blood Clot from the Pill? Help!

Vanessa
I'm currently on my period after starting my first pack of birth control pills, and my right leg is aching around the calf and the ankle/feet area, similar to the growing pains I had growing up. 
To be fair it started the night after I began excercising for the first time in months which could be coincidental, but it's been three days and the ache is still there and only on my right leg. It intensifies at night too. 
Does anyone have any experiencewith  blood clotting caused by birth control?
Also, my period this month has been 90% black or brown clots and 10% blood/old dark blood, if that os any indication on how the pills are effecting my body.