If your vet tells you it's nerves, one thing you can try is Feliway. It's a scent that mimics the "this is a safe place" scent that cats generate in their facial glands. You can get it as a spray (for bed, collar, carrier) or a rechargeable plug-in (Kitty Incense!) They say humans can't smell it, but I have a really sensitive nose, and do occasionally catch a faint whiff of cedar/coconut when I'm right next to the diffuser - if you can smell it at all, it's actually quite pleasant.