My experience has been a lot like Jill's although I'm still very new to all this. Our son was diagnosed with ADHD about 2 1/2 years ago, but the Autism Spectrum Disorder diagnosis didn't come until about 6 months ago. That felt like a lot of work and a long road.
However, having a diagnosis is one thing. Knowing how to help your child is an entirely different question.
Our son has gone to a social skills therapy, receives speech therapy (which includes social language and can be so much more than making sounds and articulation) and occupational therapy. This summer we are going to try counseling. Some services have helped more than others, and his needs do change so we have to be ready to change.
Our son was not successful in the traditional school. There are so many reasons, and a different neighborhood school might have been just fine for him. We were given the option of a school that had "structured classrooms" and 1:3 (or 4) staff:student ratio. We are very fortunate, because that school has made a huge difference in his life. (And they do not have homework! But we make sure he reads a lot.)
I agree with Jill that this can be an exhausting road. You are most likely not an expert in ADHD or in special needs, yet your son's teachers may turn to you for advise on what to do. That used to make me cry at night. I just felt so helpless! How the heck was I supposed to know what to do? I just kept putting it back on them. They need to be communicating with the special ed teachers at the school who actually do know about my son's needs.
This is going to be a little like when you had your first child. Sometimes you tried something and it worked. Sometimes you had to try 7 or 8 different things before you found something that worked. But now you have 7 or 8 more tools to try next time. Then when your second child came along, you had more tools to begin with. That second child still did things that made you ask other moms for some new tools, but you most likely also felt more comfortable and less stressed. That's kind of what's happening here. Right now you don't have too many tools, but you are learning. You are finding more and more things to try.
There are always going to be days that completely make you feel like you are starting all over again. But those days will start getting further and further apart. Keep working with him, keep talking to the teachers, tell them when you don't know what else to do. Things will get easier.