Your vet should have something that you can give him/her if necessary for traveling. Only they can prescribe what is right for your dog, a lot of people have found that these little guys travel well, Rizzo does great in his travel carrier, he's quite and usually just falls asleep. Have you crate trained your dog? If not it would be easier on him to get him started by putting them in a crate for a short period, and then increasing the ammount of time they spend in there so they're used to the crate when it comes to flying.
Have you looked into flying with them in-cabin? That's usually best, and sometimes flight attendents will overlook you pulling them out of the carrier and placing them in your lap if you place a blanket over them, which also helps them to be calm.
Good luck with your travels
