but if you're doing them to the point of muscle exhaustion and not stretching afterwards you could be making your shin muscles very very tight. You *must* stretch them. Remember that your muscles go in opposites. Stretching the front of your thigh will also stretch the back of your calf and vice versa. Any stretches where you point your toes as far as you can during the stretch will also help stretch out your shins.
Try searching online for a Brook's or a goodfeet store near you. I would say you could do their little online questionnaire, but since you probably don't know what kind of foot you have it's best to let a professional check them out first, then you can adjust as you see fit.
www.goodfeet.com
www.brooksrunning.com - Type in your zip code in the dealer search box and start calling the vendors it brings up to see if they do professional shoe fittings and gait scans (they scan your feet as you walk to get an active view of pressure spots and how your foot spreads so they can get a better fit.) Most of the shops that carry Brook's are specialty shops for competitive runners so they usually have experienced fitting professionals on hand.