I think yes, it's part the teeth coming in, but I also think it takes a bit longer to catch up from OT at this stage (I don't know if it's the one nap thing or just because they're more active, but that's what my experience has been). Also, all the changes this week are sure to play a factor as well.
In terms of the teeth, I'd give meds 45 min before nap and bedtime. I usually do this for about 5-7 days in a row and then 'try' to take about 3 days off. I do acetaminophen before nap and ibuprofen before bed. Then, I think you have the right idea to pull back on nap time and bedtime when possible (he could only need 15 min early, but maybe up to 30 min). I know that may not be possible with a nap at nursery, so you'll just need to stick to the early bedtime on those days. And it may take several days in a row to really catch up from the OT he's built.
One other thing that most likely won't be possible with nursery and may not work for him, but did for my DD, was to go back to the morning CN (no more than 20 min) and longer pm nap when she was really OT. He's on the younger side of one nap, so it may work, but it does seem like one nap suits him. When my LO had a really tough night with teeth and an EW, that was the only way to get her through the day.
Big (((hugs)))! You've got a lot going on it sounds like. Hope something in there helps.