What Could Bruise In Gluteal Cleft Extending To Buttock, Leg And Ankle Indicate?

About 6 months ago I noticed what appeared like a bruise beginning in the left gluteal cleft & descending down my buttock. Over the months it has extended slowly down my entire leg to the ankle. It does not hurt & is not palpable. It seems to follow a venous pattern. I took birth control pills for 3 months before this occurred & I take a multivitamin with iron daily. Other than that nothing is different in my health. I am 45 years old.