Sounds like it's possibly the same IT band issue I've had for over a year.

http://www.itbs.info/
http://www.drpribut.com/sports/spitb.html
http://www.lwcoaching.com/library/runnersguideitbs.htm


It used to appear like clockwork at about 25 miles, but with regular stretching,
http://www.rice.edu/~jenky/sports/itband.html
http://www.rice.edu/~jenky/sports/itband_str.html


foam roller,
http://www.youcanbefit.com/ROLLER.pdf
http://www.kneeguru.co.uk/kneegeeks/8732548401.html


and strap,
https://secure.cho-pat.com/products/...roduct_type=27

it now doesn't appear until 75 miles.


Good luck.