if it hurts the skin right around the top of the boot, i would look to your socks for the answer. if your socks are too short, the may may being ripped out of your legs. if your socks all tall enough but super thin, you might want to look into thicker socks.
if it is hurting the muscle in your calf and the bone in your shin, your boots are probably buckled way too damn tight.
if the problem is just due to pain from backseat landings, try booster straps and buckling your boots a bit tighter.