Thanks for your careful description of symptoms.
Symmetrical rashes of the kind you describe are often either allergic or viral in nature. The fact that your rash is localized (not all over the body) makes allergy quite unlikely, as does your reproductive doctor's unfamiliarity with it. (Generally, specialists get to know the likely side-effects of their particualr corner of medicine quite well, because they get calls about them.)
In many cases, funny little red rashes with bumps and blisters come, last a few days, and go away as mysteriously as they came, leaving no trace or consequence.
I think your nurse practitioner should evaluate you for any other evidence of a viral infection (other symptoms, white blood cell count.) If no other evidence is found, it may be hard or impossible to tell what this was by the time it goes away. This is certainly not the rash of rubella (German measles), to which you were presumably immunized anyway. That's the virus, as you may know, with potential risk for babies.
If it turns out you are pregnant, I suggest that you have an obstetrician, dermatologist, or experrt in infectious diseases look at you. Good-quality photos while the rash is fresh may be useful as well.
In other words, I doubt that you yourself are at any risk; the risk to your pregnancy, if any, is also probably very low, but needs the evaluation you are in the process of seeking.
Best.
Dr. Rockoff