I'd check the web for side effects and ask your psychiatrist. But anyone can be allergic to a medication. If you can't think of any other explanation, your doc might have you stop the med and see if the rash goes away. It's still early so you can do that, whereas it's harder once you've been on a med for a while to stop taking it. Also, side effects start before effects do, and they sometimes go away with time, but this is an odd one at least to me.
Just thought of something -- it's just become winter, are you wearing something such as wool in that area you might be allergic to?
All types of medicines react differently to individuals and have side effects. If you observing these rashes only after medication, you should call your doctor.