What Causes Bruises On My Calf And Back Without Any Injuries?

hi, for the past couple of months i have been getting bruises on my thighs and calfs without any memory of bumping into anything. This can sometimes be up to six on the same calf and between 2-3 large ones on my thigh.I am also experiencing alot of lower back pain. I am 30 years old on no medication, fairly active and a size ten.