Your son's needs/wants likely changed to something not available at daycare
Without a lot of additional information, it'll be difficult to state definitively what the problem is. But I'm guessing you're super tired, so I'm going to advise on where to direct your limited mental energy.
As you're probably aware at this point, once you start figuring out your son's routine is right when he changes it on you. Given how much children vary between one another in the first 2 years, I've almost no chance at guessing exactly what your child's specific wants/needs are at this point in their life. When my daughter was 8 months she wanted to be held all the time, when my son was 8 months he wanted to try and walk to keep pace with his sister. However, assuming competent daycare teachers, then they've already exhausted the options of attention, play, reading, distractions, diaper, and other things that are 'free' for them.
Thus, I suspect your issue lies in something(s) available at home that aren't available at daycare. Turn your attention to what supplies you typically provide to the daycare to expand the options they have available:
- Do you typically provide them with 3 bottles for the day? Might need to go with 4 or 5 if your son's having a growth spurt.
- Has your son taken to preferring a specific toy? Make sure that goes with them in their bag so that they can use it. One can only guess why your son needs to see his lambie between the hours of 3 pm and 5 pm, but it's unlikely you'll be able to persuade him otherwise.
- Is your son teething? May be necessary to send with teething rings along with some infant motrin and doctor's direction on how much to administer and when.
These are just a few possibilities, but there are many more that could be applicable. I'd advise you to think about what your son's current needs are, how they're addressed at home, and ensure those solutions are available to the staff at daycare. If you come up with several ideas, try them all; it's entirely possible that there's several causes.
If you're tired all the time, it means you're doing a good job. Good luck!