Help. My poor boy has had 3 accidents in the last 3 days (2 night, 1 day) and has been super fussy. Is there a milestone that involves regression from potty training?

How can I help him? He is really embarrassed by these accidnets. He is almost 3, been potty trained for 11 months (no accidents for several months and before his accidents were all preschool naps).

Thanks!