Katherine - amazingly big hugs.
Point from me, please remember not to think about it so seriously Hon. I know OT kids are awful and I am so much like you panicking even before nap started, than when it is short - I will have a OT baby:D LOL. But on the other hand, they cope somehow. Ha - some kids sleep 8-9h at night and they parents think it is ok, and they still cope somehow.
With such a great and caring mother like you, I believe that you will figure it out or he will figure it out and one day (hopefully very soon) you will just have once again a happy and well-rested baby. For now maybe go with the flow and try to relax - rather than planning what to do.
And... You know that nursery (especially the beginning) it tough. We both know it. But it's just a phase - at this age, probably a short one because he is old enough to adapt quickly. Look at my posts from September when I was moaning about F in nursery not sleeping well. Gosh - nothing helped. But we survived, F is happy and coping amazingly well in nursery now. I am sure B will be fine very soon.
On the other hand, except from sleep - how he is doing there? What the nursery ladies tell you:)? Is he social? Is he eating well or rather a picky-little munchkin:)? Is he playing well there? Is he a small leader of the group or rather a friend-for-everybody type of a boy? Do they teach children something there? We have ie English lessons LOL where they are singing English songs - for sure F will be fluent soon:).