The usual cause is high-heeled sneakers coupled with a heel landing. Given your weight, they almost certainly sold you a lot of cushion. That's bad. Really bad. Were it me, I'd go completely barefoot. This site has lots of useful advice:
Begin Here!! « The Running Barefoot
And no, you don't need cushion. In fact, the heavier you are, the more cushioning will mess you up. Flyweights can get away with anything.