Chancroid normally appears in the place where infection occurs. Oral sex exposes you to gonorrhea, syphilis and herpes, but the real risk is very low. Honestly I think you are overreacting. Your doctor shouldn't have given you treatment just because you were worried.
You should test as follows:
-3 weeks after the encounter, test for gonorrhea.
-6 weeks after the encounter, for syphilis, and if you get a negative result, repeat it 3 months after the exposure, as there are people that take longer to show a positive result.
-3 months after the encounter, test for herpes.
Try to relax, as the risk is low, and getting nervous is not going to change the final result.
All the best.