It is my understanding that allergies usually present the first time you take something. However people have been known to worry themselves into reactions if they dwell on it. So use your copping skills to reduce the worry about reactions to the meds and trust your team. It sounds like you have a superb T.

The best indicator of future behavior is past behavior, and you did well in the past on getting a handle on your thinking, you can do so again. It is possible things will come up in the future but again you know what you need to do to get a handle on it. You also learn from mistakes, you know now not to go off meds without the docs help. Worrying about the future will not help you today but working on your current problems will help any situations that come up later. Talk to your T about projecting your worries into the future and ask for help in living in the present. It's a skill called mindfulness. An easy idea and a hard skill to learn, but a worthwhile one.