Blood allergy test negative to p. chrysogenum, always told im allergic to penicillin. i even had rash with ceftriaxone. how to interpret this?

Rash may be viral: You may have not had a true allergic rash to the cephalosporin, but rather possibly a drug rash associated with the underlying viral illness that you were being treated for with antibiotics. Either way, there are other choices; for now, it seems reasonable to state allergy to penicillins and cephalosporins until such time that you may actually needs them, and then we can do challenge testing.