Any idea why our dog has been behaving like this?

[Saltire]

4 year old Border Collie.
For 2 days now very unsettled, keeps going to front door, pacing around and whining.
When he's out for walks (he had 5 yesterday as I thought he maybe needed out hence the whining) he is fine, he runs and plays and pees and poos normally he's not off his food or water. He slept all night never heard a peep out of him, I even left my door open so I could hear him. Then at 8am he started again. He ha sben out this morning, and the back door is currently open.

We had visitors last week (and the dog hasn't seen DH for 6 months), and he tooka bit of a shine to the male guest. Is it possible he's
A- missing the guests
B- ill
C- knows DH will be home soon

or something else

Fireworks have started here, do they worry him normally? He can probably here ones you can't. Or have you been stressed about visitors and he is picking up on it?

Could be a female dog in season, that he can smell and no human can?

I'd say fireworks, he's probably heard them once, and now everything is making him jumpy.