Started doxy 4 days after possible exposure to syphilis (giving oral, mouth entrance point). also rocephin 500mg shot 5 days after exposure. doxy is 7 days 200mg/day. is this early enough to kill/prevent syphilis incubation and not become contagious?

The antibiotic course you were given is for gonorrhea and chlamydia exposure, not for syphilis. You should be treated as an early syphilis case with Penicillin G benzathine 2.4 millions unit x 1, not Rocephin one dose. Because you also receive doxycycline so it should cover early syphilis however the course should be 2 weeks. The abx course you were given is for gonorrhea and chlamydia exposure.

It should be. But to make sure pl get tested under care of your doc. This is risky behavior