TL;DR: Skip to the last paragraph.
So, I studied psychology in university and this is to the best of my knowledge.
IQ is basically scientifically outdated and based in racism and classism. The guy who popularized IQ testing in the US, Lewis Terman, was a horrible racist who loved using it to prove White people were superior to black people. There are much newer theories of intelligence that view it more as a domain-based thing (e.g. someone might not be musically intelligent, but they might be mathematically intelligent and so on).
There are also different ways your score could’ve been thrown off, too, especially if your ADHD is relatively severe. Unless you have some sort of developmental disability like Down syndrome, it’s actually pretty likely your IQ is roughly the same as your siblings’.
Honestly, the real issue here is the ADHD. Take it from someone who also has it: if left unchecked, it can be a life-ruiner. I was a B and C student and had no clue why until I was almost 23 and finally got diagnosed. I got into university, but it was only after spending 4 years in community college. The guy who diagnosed me said that he doesn’t know how I actually managed to do it. He said it was like I had been trying to swim with cement blocks tied to my feet.
Forget intelligence for a second. You are very obviously an capable person. You worked hard in school, you have a good command of the English language, and you’re holding down a job in fast food (a field that sent me to tears multiple times, mind you). Your problem is that you’ve had a very rough life with little support. Prioritize kicking your addictions (maybe try and find a recovery group). See a therapist to talk through your father’s abuse. See a psychiatrist to talk about medication for ADHD (non-narcotic, of course). You deserve to be satisfied with your life, and I believe you can get there.
I think the original commenter suggested autism because of OP’s rather… peculiar hyperfixation. Hyperfixations on atypical things are common in people on the spectrum.
To me, it’s either that or OP is very very young.
EDIT: also, star trek rules