If you also have a 6month old at home, he may be reacting to the baby's being in a diaper and the attention that the baby gets. I'd make no big deal out of him soiling his clothes and a REALLY BIG DEAL when he goes in the toilet. He has shown that he can do it at the daycare. I bet it's a passing thing. I know you are tired, but just try it.
I am currently raising 5 boys ranging in age from 17 to 18 months old, I can say by my experience that the avg age of potty training that i have experienced is around 4 (without pushing the issue) boys tend to take a bit longer than girls, but IMO they are so busy with activity they wait til the last minute to go and end up having the accidents. I offered a clear jar of tootsie rolls or dum dum pops in the bathroom and everytime they "actually" used the toilet they got to pick a treat. It worked for me. My son who turned 4 in March is for the most part night trained now, we have the occasional accident but mostly due to me not following up on his using the potty before he falls asleep. Make sure to limit their fluid intake, which I'm sure you are doing and offer positive reinforcement, and trust that they will get it when they are ready.
On a side note, Pull-ups are a waste of money, they feel like a diaper and offer no incentive to use the "big boy potty", kids need to feel the "uncomfortable" of wet pants. You will end up doing more wash but it won't be for long.
Good Luck
Since he is going at daycare, that means that he can control it. If he's not going at home, its because for some reason he does not want to go at home-- most likely for attention or to keep from letting go of his parents in some way (although most likely unconsciously.)
If he has demonstrated that he can do this, then I would take the hard plunge of simply not allowing him to wear diapers/ pull ups at home -- and just matter of factly indicate that's the new rule, and then be done with it. If he goes on himself, well, then he will get wet or dirty -- which is very uncomfortable. After a few days, I am sure he will stop, since he has already got the hang of how to go potty because of day care.
This is what we did with my son. Instead of rewarding or cajoling, we just said one day "Thats it." He was done in about 4 days.
him going at daycare and not at home is probably b/c he sees the other children going and he does not want to be embarrassed. he hears them asking and seeing them go use it and wash their hands and he's picked up on it and is following their lead. perhaps, at home in his comfort zone, he doesnt feel a need to impress or follow and doesnt care who sees