L.A.
I agree with a good nap. And at least 1 hour of very active play in the mornings and again in the afternoon. Running jumping, climbing peddling.. He has a lot of energy and needs to use it up. Running errands is not a physical activity.
It gets darker later, so if is room is still bright, you may want to consider putting up something to block out the light. I used to hang up quilts.
We also found if turned down the lights all around the house and made sure the TV was off, so it did not seem like anything else was going on it helps your child not feel like he is missing out on anything. Speak in quieter tones. No rough horsing in the tub or while drying him off.
Also if there are neighborhood noises and sounds, that could also be sounding interesting to him.. Kids laughing, people talking, car doors closing. Maybe a nice sound machine or some quiet music.
When you read a "bedtime story", this is not the time to engage your son.. Do not ask him questions about the book. Do not get all animated with your voice. Read it in a quiet tone and towards the end of the book, begin reading slower and slower.
Remember vitamins need to be taken in the morning with food. They pep up a lot of kids, so if you give them at night, it may be too much of a stimulant.