I too have been diagnosed with FHL tendonitis. It is a flexor of your great toe. It attatches to your big toe and originates along the smalller leg bone or fibula. Its course is then more medially and under the inside or medial ankle bone. Very common with over pronation. So like the other posts have mentioned...good arch supports or stability shoes can help. Stretch the FHL by putting big toe up against the wall so it is elevated then combine a bent knee runners stretch. Can also use a magazine rolled up under big toe with runners stretch. In addition...why are you over pronating? Do you have week hip abductors? What about hip rotators? Hamstring flexiblity along with other posterior mm should be stretched as well.