Well we can catch STI s from oral sex, but they would not likely show up so soon
"within hours "
However - I presume there is some intense mouth to mouth kissing, before / during after -
so you may be acquiring “ordinary” germs, flu like germs. ( gonorheah and herpes can be also spread oral to oral probably there are more )
Or you just might be in a awkward position, straining yr neck - yes this can feel like
a very sore throat. leading to a general body reaction
I would urge you and yr partners to be tested for STIs - If in doubt : get tested.
LINK TO COLUMN: Can I catch an STI from oral sex? - The Straight Dope