5.5 month old is a totally different baby!

I’ve been searching reddit for the past 3 days trying to find something that can give me answer to no avail so here it goes.

First, my LO is 24W6D, almost 6 months. He was always a great nighttime sleeper, always was put down and with us being close by, would fall asleep without help. Would sleep 10.5-11 hours a night with 1 feed since about 12 weeks. Even when the 4 month regression hit, his inital falling asleep for night was alone - he woke up a couple extra times a night for a couple of days but that was that. Always in bed between 7:30-8:30 after routine (bottle, bath, pj, story, crib) and wakes up 10.75 hours later (6:15-7:45).

I was an EP and decided to switch to formula last week since he’s always had really bad spit-up and reflux. He took the formula very well with no complaints.

When it came to naps, he used to need to feed to sleep and only contact napped - we could never put him down - until he turned 20 weeks when my husband stopped feeding him to sleep and he stopped that association. We also started being able to put him in his crib for nap time and with the same as bedtime, with some closeness from us, he would fall asleep. He was always a crap napper so between 20-40 min alone, could go to 1hour contact.

Fast forward to this week, out of nowhere, he is REFUSING his naps - will scream bloody murder anytime you attempt to put him in the crib, and even trying to rock, contact, feed to sleep, nothing works! Nightime is still great, still put into crib and he falls asleep - however, he has been waking up for the pacifier more often, and also due to rolling over and getting stuck.

We use Huckleberry for the sweet spot nap times and that had been great. We had been transitioning from 4 to 3 naps. For the past 4 days, he will NOT nap unless I put him in the car and drive. His WW are 2/2.25/2.5/4 ish (the last nap was always a mess) but since his naps are short, the schedule is usually super messed up.

Obviously, he’s been super cranky and fussy, we are also thinking teeth? What is happening?! Do I need to sleep train?

TLDR; 5.5 months, won’t nap anymore (contact or not) but fine for nightime.