Further, 2 days is too quick for symptoms of most STDs, with the uncommon exceptions for gonorrhea and perhaps herpes. Chlamydia symptoms
rarely if ever start sooner than 7-10 days after
exposure. As for anal "discomfort", I'm not sure exactly what it means, but it seems unlikely to be related to receiving analingus, although I suppose it is possible.
Accordingly, if STD explains your symptoms, most likely it was acquired from your regular partner.