I do not have this problem all the time but yes, sometimes the shower is almost unbearable. I guess, when I do it I just repeat to myself over and over that the nerves will calm and it will be more comfortable. I use the shower quite often to desensitize the area also. If I personally had to pick between a rub down desensitization and the water doing it for me, the water is a much greater relaxor.
I hope these thoughts make sense.
Gentle Hugs,
Rain