Sleep regression or something else?!

My 11 month old little guy has had a rough couple of days in general but mostly with sleep. He has been sleeping about 9 1/2-10 hours at night but there has been more and more crying. only took one 45 minute nap this morning and completely refused afternoon nap - there was a lot of screaming. He had been awake for 7.5 hours so fed him early and finally got him down with a bottle at 6:15. Woke up exactly 45 minutes later... screaming and I mean screaming! We let him go for 15 minutes but it just got worse and worse. I went in and got him and he would not settle down until I took him out of his room. He is beyond exhausted and fussy but otherwise seems ok. He seems to be waking hysterical at that 45 min mark no matter what we do. We checked all the typical pain issues. Could it be something else? Could I be missing something? Or just a regression? I’m beyond exhausted and so is he. I’m at a loss. He has been sleep trained since 8 months but obviously that’s been out the window as of lately and we just do whatever we can to get him to sleep...