What Can Be The Reason For The Pain In The Leg?

hi, im 17 years old and im experience odd pains in my legs. i run alomst everyday and have been for years. all of a sudden while i run and after my calf muscle and below turn this odd blotchy red color. and when im not exercising my calf muscle is always stiff. i dont think its pulled, ive pulled muscles before. but its starting to freak me out that the red and purple blotches wont go away.