I second this and what was said above. I have gotten slight bumps where the cheek means the chin when using a razor that hasn't been honed well enough. I have also had this happen with my Gillette SS when my shaving angle or speed is off. I would not call it a rash. More like irritation/razor bumps. After a two or three days it usually goes away.
I would try changing up blades and paying close attention to the basics. Angle, speed, skin stretching.
Westcoastshaving.com sells sample packs if you want to try a variety of blades to find what works best for you.