So if you have tried meds I'm assuming he is teething then? Teething always caused major problems for DS1, even with meds. So that could be part of it.
Also, I wouldn't let him nap that long, even if he does have short nights, because he's just making up for it during the day. I think 2hrs max should be good for a nap, definitely not more. Hopefully you can talk to daycare about making this happen.
We've had similar problems around that age and I could never really put my finger on what was going on. Things did improve initally after DS1 finished getting all his teeth, then they got back again right around 2 years old. We spent awhile adjusting his bedtime routine, giving him more time to wind down after his bath, and spending more time with him in his room. At first it was hard, he wouldn't let us leave at bedtime and would wake in the middle of the night and just wouldn't go back to sleep. DH ended up sleeping in his room every night after he woke, which obviously we didn't want either but we were just so tired and had DS2 to deal with as well.
What does your evening bedtime routine look like? I think the bedtime routine is very important especially at this age. Also, since your LO is in daycare I wonder if he is feeling like he is missing out on mommy and daddy time, so is trying to make up for it at night. I know for us, evenings became so hectic. Even though I am home with the kids during the day, I think DS was missing daddy, and when we were rushing through dinner and bath to get them into bed he started to feel overwhelmed. So we changed things to make sure he gets more daddy time in the evenings and it seemed to make a difference.
Anyways, at bedtime I would stay in his room and comfort and talk to him until he felt comfortable again, and the phase seemed to pass on it's own.
We also decided to move to a BBB at this age too. I know it's really early for some people, but in our case it actually helped as I think DS felt more comfortable in a bed rather than his crib. We actually started by just putting his crib mattress on the floor for a few weeks, then when he seemed to do ok with that we got him a bed.
Well, that was a really long post that offered very little advice! lol Guess just wanted to say we have been there too and lived to tell the tale. (((hugs)))