Most of what you’re asking needs to be answered by a professional through a thorough evaluation. While autism is commonly diagnosed that young, ADHD is not. The current diagnosis guidelines are for kids over the age of 4. I know it is sometimes diagnosed younger, but that’s not the recommendation of the American Academy of Pediatrics.
At ages under 6, the recommendation is to try therapy first, then move into ADHD medication if necessary.
Getting an evaluation will provide some answers and guidance.
ADDitude Community Moderator, Author & Mentor on Parenting ADHD, Mom to teen w/ ADHD, LDs, and autism