18 month old suddenly waking and wanting to nurse all night after starting daycare

This is actually really common after a big change such as starting daycare. It's a lot of separation from you during the day now and sleep is also separation. Our babies are evolved to be in relationship with us, not independent from us at this age, so they often seek more connection when more separation is introduced. There's also the possibility of molars coming in and those are a beast all on their own, regardless of other big changes.

Something you can try is a dedicated 5-15 minutes after getting home (or more, depending on what feels right for you and your baby) before bed, no phone or screen or any distractions, just you and baby getting some quality time in to help him fill his connection cup. If it's molars, pain meds may help. My son has his molars coming in and when we don't do motrin before bed, he's latched allllll night long. I feel like we've been doing motrin forever but when we don't do it, he wakes up a lot more to relatch so I know his teeth are bothering him.

I don’t know. It doesn’t feel right but maybe it’ll get us through faster. My brain is too tired to think clearly

We had a bit of this when my girls started daycare. They only go twice a week but both the three yr old and 1 yr old started having night wakings. It actually took the 3yr a long timw to get over it. All see need was a hug and to be tucked back in but its still exhausting. If the nursing is something you want to back off of i would start slow and gentle... what's best for you but but you have to find what's right and works for you best and work on the connection in other ways