Been there; done that.
I have a now 40 yo with many of the problems OP describes in addition to health and mental health issues. In order to complete his college degree (which required numerous short enrollments over an extended period of time) he did a research project based on his experiences. I'd like to share some resources he found helpful.
National Alliance on Mental Health
https://www.nami.org/
National Institute of Mental Health
https://www.nimh.nih.gov
Association on Higher Education and Disability
https://www.ahead.org
Mayo Clinic
https://www.mayoclinic.org/
DO-IT
https://www.Washington.edu/doit/
He had an IEP in HS with a gifted IQ; it took 12 years of public and private school for him to be far enough behind to qualify. A significant learning disability was not detected until he was in 8th grade when he was in a university based tutoring program for K-12 students having school problems. In his case, he has an auditory processing disability; he hears but does not remember what he has heard. He needs information to be provided visually. A neuro-psyc exam needs to be discussed with PCP and other current health/educational services providers. Also discuss a sleep study; in my child's case, many of his physical health problems can be traced to a serious sleep disorder not diagnosed until he was an adult.
College was even worse than his HS experiences. A college degree is required for him to work in the area of his greatest talents and interests. Be aware of requirements to qualify for disability accommodations at the post secondary level. Remember that the goal is to have a self sufficient adult. Mine is still a work in progress. The goal is simply to pass the next milestone along the way not ace the exam.
Also be aware that serious mental health issues frequently appear in late adolescence. After having dealt with a suicidal teen/20 something, I'd be concerned that the academic problems are indications of more serious disabilities that may not become obvious for years.