I can't rest and relax either which was the main objective of the trip

[ROBINDESBOIS]

I can´t rest or relax .
other possibilities.?
Is the original OK?

[Rusty]

I can't rest and relax either, which was the main objective of the trip.

Other than the missing comma, you're original sentence is great.

I can't rest or relax, which was ...
I can't rest, nor can I relax, which was ...
I can neither rest nor relax, which was ...

[Awaken]

Is this sentence being said to someone on the phone/email/chat while you are on the trip?

[Perikles]

I would say "I can neither rest nor relax..." and all the others above all sound a bit odd. Perhaps it's just another BrE/AmE thing. :thinking:

Other than the missing comma, you're original sentence is great...*cough* Would you like to revisit your typing? :D

[Rusty]

Oops! And I try so hard, too.

[ROBINDESBOIS]

Awaken, I know what you mean *the agreement*.