What Causes Pain In Calves After Walking?

I am a 25 year old male that is battling with an issue of agonizing leg pain when I walk a block or so. After a brief rest I am good to go. I have been diagnosed with high blood pressure. I barely walk distances outside of what someone does in a home, and for the most part am very sedentary. I am worried about this being a case of intermittent claudication having a very grim outlook on my cardiovascular system. Tonight I did a experiment, I walked about two blocks and I had the horrible pain in my calves. I rested for 15 minutes and then walked 2.5 miles with minimal to no pain at all. Am I overreacting? Does the long walk with no pain following the painful one exclude me from claudication?