First, see a nutritionist, email me privately and I'll send you a name,
Second: It would be prudent to get a neuropsych exam at Our Childrens House at Baylor or the equivalent of that, wherever you live.
That said:
Third and most important and the hardest thing to hear! In general, boys are often not ready for these formal group settings. Consider his age. Really, kids are not meant to sit quietly and listen at pre school age, especially not boys All children develop at different rates. Putting kids that are not developmentally ready into schools and school like settings has had a considerable impact on our society and created a thinking pattern that it is acceptable to medicate small children ( so they will "behave")
Your kid is crying out to you with his behavior. Spanking him and punishing him for reacting completely normally will really confuse him. Think about it.
What is he? 4? Remember being 4? Nope, neither do I. Other than I know I was not in a school setting and my mom was always around and I was encouraged, not discouraged to explore and move about and play.
I urge you to take a long hard look at your life. You have a child. You are barely with him. I understand what it is like to have a career, work all day and have a child. You have to make some hard decisions. Do you want your child raised by daycare? Do you want to have to deal with these problems because believe me they will keep happening. Your kid needs YOU.
I urge you to re evaluate your life. Being a mother IS a full time job. I had to re evaluate and when I did, I walked out of a lucrative career because my child needed me. You bet it is hard. Our entire lives changed when I did this. Our financial picture is certainly not as rosy as it would have been had I kept growing in my career. My son is 12 now and I can tell you,it took me until he was about 6 to see I was the only one who could make the difference in his life. I will always wish I had not waited that long! I'm not saying you can't work, you just need to think about how you want to work. Are there things you can do, ways you can change your career path that will enable you to perhaps work part time until he is in school? Perhaps you can take a different path to be home with your child during these crucial years. You will be glad you did. I know I am.