I recieved oral from a man, and then within 4 hours later had sex with someone else. i think the oral gave me a yellowish discharge. is it contaious within the 4 hour window? both people claim they have no symptoms. is it possible its not an std?

Get tested: It is unlikely that an std would show symptoms in 4 hours, generally it takes days to weeks for them to take hold once you have been inoculated. The discharge if it is an STD came from before the oral sex. As to what the discharge is, get checked. And yes, you probably may have passed it on to the other person you were having sex with if no protection was used.