Leggings keep getting holes .. help!

[Supermagicsmile]

I seem to go through leggings at a ridiculous speed. They always seem to get holes in the croch area and I don't know why!
Am I doing something wrong? I have now started buying cheap pairs from Sainsburys to save money.
I wear leggings every single day with every outfit so they do get a lot of use but what can be small holes in the morning can be huge by the evening as the friction when moving seems to have made them worse.

Where can I buy cheap leggings that may not get all holey?!

[Niminy]

Try buying a larger size. If they're holing around the crotch it's probably because the seams are being pulled.