I have a question about a possible syphillis symptom, exposure and testing.

21 days ago i recieved brief, unprotected oral sex from another man, and this is the only sexual activity that i had this year.

Fast forward to yesterday:

While masturbating I felt a sort of friction burn pain on the upper side of the penis (on outer, upper foreskin somewhere in the center of the penis)

I noticed like a tiny raised area not perfectly round (~4 -5 mm) that had a hard dark coloured scab ln its center. That tiny scab fell of while i was showering later that evening. 

Today the skin change is pale in contrast to surounding skin (like it has chaffed off on that little area) and it does not hurt nor ooze. When i touch it it feels just like surrounding skin and its not hard. It seems that it hasn't grown since yesterday, and I'm pretty sure that skin change was not there 2 days ago.

 So, I would like to ask you if this does sound it could be primary syphillitic sore? And if so, when should i go for the blood test considering my exposure was 21 days ago. 

The test would probably be TPHA or TP-EIA.  

To mention, I have never had any such skin changes on penis. 

Thank You in advance!