You might also have an angle issue. ATG can be very uncomfortable if you have the blade at too steep an angle. Stretching your skin ATG is also important. Make sure you are stretching the right direction or it will make the issue worse.
+1 on the angle. ATG pass should be made (I think) with a watered-down lather and less of an angle than the WTG pass. And stretching cannot be over-emphasized.