Hi Cathy
Maybe he's just being tired out more spending time running around with the other 2? I think you are doing the right thing just checking his temp etc and keeping an eye on him, but it probably is just a phase. And lucky you! Baby Picky (age 2) has been awake since 4.50am and still hasn't slept a wink for the rest of the day. Think he had a nightmare as he's such a good sleeper normally, but he is like a machine today! Not great when I'm 26 weeks pregnant and valuing every second of my sleep!
I'm sure everything will be fine
Px