Potty Training Derailed

I am probably totally overacting...ok I know I am.  We started potty training Hudson in October or November of last year and he caught on so quick we were shocked, we let him lead the way we did not push him one bit. By the end of November he was even staying dry all night so it came to a shock to me when a week before Christmas he started to have a wet diaper in the mornings (when we started potty training we went straight to underwear all day and diapers only at night).  I thought well it is probably because of the holiday coming up and maybe he is just really excited and cannot focus.   Well, every morning since he has had a wet diaper in the morning.  And now that he has turned officially 3 years old  he has been having accidents throughout the day.  I am just so stunned because he was doing so well that I never had to worry about accidents while we were running errands or while he was at school for 2 hours.  Ok yes we did start him at a new school so just last week so  I guess that could be causing this regression.  I just never thought in a million years this would happen, why I have no clue I guess I thought that he would not be phased by this change.  I just want things to go back to how they were!!!  No accidents!!!  I hate feeling frustrated with him because I don't want him to feel bad but I am just so...well....frustrated!!!  I guess I just need to take a deep breath, drink a glass of wine and go back to step one of potty training where I just ask him if he has to go every 2 minutes.  Has anyone else gone through something similar?  I would love to hear from you!