First,
tetracyclineTetracycline
Tetracycline hydrochloride
Tetracycline topical is not effective against trichomonas; your boyfriend will have to see a health care provider. His rash isn't due to trich, and probably not an STD.
Not every case of trichomonal vaginitis causes odor. But still I'm nervous about your diagnosis and I wonder about your doctor's knowledge level in this area. Most important, Duracef is not active aginast yeast; if you really were given that drug, either your doctor badly misunderstands the treatment of yeast infections or you actually had something else. Second, the Pap smear is a poor test for trich; most apparent positives probably are not accurate. (On the other hand, maybe the diagnosis wasn't from the Pap itself. Your doctor might have sent other tests at the same time as the Pap.)
But assuming your trichomonas diagnosis is accurate, either you or your partner might have carried it for 2-4 years. And if it isn't an STD at all (maybe it's all yeast), there is no implication about other partners, On the other hand, you know your boyfriend and I don't--i.e., you are in the best position to know whether he might have had other partners.
You should double check all this with your physician; or if you share my suspicion about his knowledge in this area, consider trying another health care provider.
Good luck-- HHH, MF