I would check on the shoes and then have a running store look at your stride. I used to hate running because in general it hurt. I tried a bunch of different shoes, settled on Brooks Ghosts, and running is actually a pleasure. I also focus on my stride and work on foot strike, length of stride, etc...

Since you're doing the C25K I'm assuming you are not super athletic to start. If you are overweight, you may want do some other cardio until you get your weight down a bit. If it hurts obviously don't do it and find some professional advice. Re-doing days in a training program is fine, everyone has their own pace.

Good luck!