Originally Posted by
phlydude
when I got it, I wasn't sure - my sit bones measured 153mm and they told me the 155mm saddle was the right one.
This is definitely the biggest factor. The Specialized saddles all have a downward curve in the rear that reduces the effective width that you can place your sitbones. Example; a saddle listed as 143mm wide actually has a usable sitbone area of 133mm. Get something wide and flat and your issue should go away with time.
The B17 looks to be @170mm wide so it will definitely help.