When I was a baby, I was allergic to erythromycin. Is it possible that I am not allergic to it any more?

Yes. It is common for babies and young children to develop a rash with viral or bacterial infections; often, when a child with an infection gets treated with an antibiotic and develops a rash, the antibiotic is blamed. Discuss your situation with an allergist; it may be appropriate to do some skin testing or test dosing to determine your true status with regard to erythromycin.
Very possible. Most intolerances are mislabeled as allergy. Ige reactions are rather rare. An accurate description of your reactivity would be crucial.