Its only going to get worse from here unless you step in and do something. As others said, get a professional neurospsych evaluation, followed by specific recommendations with an IEP.
Since your son is already in high school, trying to get accommodations for standardized testing (ACT, SAT) will be viewed with skepticism if done at the last minute. If you wait until 10/11th grade to ask for extra time/accommodations, you will likely be denied. So this is another reason to get started now.
There is a subforum here for LD/ADHD, definitely take a look