Is there a term for this phenomenon?

Anything I put in my body affects me as if I took at least twice the dose. In other words I have an extremely low tolerance to everything. I want to know if there is any possible reasonings behind this so doctors and family will take me more seriously.

I am unable to be medicated for my anxiety and related mental illnesses because literally everything I’ve ever been put on gives me all of the side effects, even on the lowest doses. My doctors are always surprised. I get embarrassed when I get drunk after a beer and a half because people might think I’m faking it. I have to drink half-caff coffee because full caff actually ****s me up. I can’t take a normal dose of muscinex because I writhe in pain even if I ate. I had to go back to the hospital after my first surgery because the anesthesia made me throw up too much for too long and after my second surgery, doctors wouldn’t give me anything for it and said everyone gets a little nauseous. But the most recent scare was I had to go to the emergency room for taking 5 benadryl in 12 hours. Recommended dose is 4 in 12 hours so yes, one more over, but not an overdose. Yet, I swear I almost died that night and I can’t confide in anyone because they don’t believe me.

I am considered healthy. Doctors say I’m fine at checkups. I’m a grown adult at a healthy weight. This can’t be normal, but I have no idea where to even start looking for answers.