oral and skin itchyness/burning but its reactive to benadryl

[Scared2112]

I have had itchy burning skin from my knees to my neck for the past approx 6 weeks (mostly in groin and chest/arm/pits), this also includes some tingling burning in my mouth.  When I returned from a short business trip to Paris I had some sleep deprivation, mildly tingly throat and was urinating frequently (no burning) so I thought I may have a little bug.  I went to the urgent care just to check to see if it was the beggining of anything.   They took some urine and swabbed my throat.  fast strep came back as negative, and urine was negative for UTI.  They then surpised me and asked if this may be an STI.  They took some urine for testing for bacterial STI infections.  They convinced me to treat myself prophylactly just in case.  So they gave me two different strong antibiotics and a pill for yeast infections (glossitis).  a week or so later I also noticed irritation on the penis (flat red spots) under the glans that didn't itch themselves but did have discomfort.  I have not noticed any visual signs of rash.  Obviously I was highly stressed when they brought up a possible STI (I had a mutual oral sex with a guy in Paris which was about 4 days before the trip to the urgent care).   Went to my normal Dr. who said it was nothing, and to stop worrying.  After that I still kept having the irritation on the penis and burning/tingling from my thighs to my chest and in my mouth.  

I recently started taking Benadryl (last 2 days) and this seems to take away the burning/tingling all over (including my mouth), and seems to be helping the irritation on my penis as well.  However when the time for the next dose comes, I feel like the symptoms are beginning again (especially in my mouth).  

My question is what allergic reaction can last 6 weeks?  is it stress?  would stress itching improve with anti-histamine?  could it be a contact dermatitis or drug allergy lasting this long?

Would a virus of any kind last this long and continue providing these symptoms?

[Scared2112]

note:  the tests were negative for bacterial STIs