Signs of allergies towards dogs

Hello , I am new here and need some advice really more opinions then advice .. 

I have had my dog going on almost four years and growing up my parents had dogs too. I didn’t ever show any signs of having allergies when it came to animals .

I sometimes pet sit my sister’s dog she lives in a wooded area she’s inside her city limits still but on the edge basically. I watched her dog around a few weeks ago and noticed I had gotten a rash when he was with me . I was also itchy but then even after he left I just felt itchy in general when I’d interact with my own dog .. does anyone here have any idea if it could be an allergic reaction ? 

I have played with my dog and cuddled with her recently and felt fine so I’m sort of confused on what had happened there .