Don’t understand what I’m doing wrong with my baby

I try to keep my almost 7 month old on a consistent schedule. No matter what he is awake by 6:30am. That’s fine. He takes a first nap around 9am. It’s usually about 30-45min. His second nap is around noon, for about 2 hours. His third nap is around 4 or 5pm, another short one for about 45 minutes. He goes to bed around 8pm. Some nights he sleeps most of it, wakes up once or twice to nurse. Some nights, like tonight, he’s restless, wide awake, and will not sleep for more than 30 minutes at a time. I am EXHAUSTED and don’t know what to do. Despite him not sleeping, he will still be ready for the day around dawn and he will still keep his nap schedule the same. I don’t understand what I am doing wrong. Why do some nights (at least 3x a week) he just won’t sleep?