Can I take antivert if I'm allergic to compazine (prochlorperazine)?

Yes. They are in different drug classes and should not cross react. However they are not usually given for the same indication. If you are looking for a good substitute for nausea a better choice would be zofran and/ or possibly dramamine. Phenergan (promethazine) is very sedating and may not be tolerated but is also a possibility if looking for nausea solution. Antivert is acceptable.
Depends on indicatio. Why are you taking compazine. Assume it is for nausea.Antivert or meclize is a labyrinthine sedative ( calms down the labyrinthine apparatus- a part of inner ear , concerned with the posture maintenance) and is used when patient has vertigo- a feeling of spinning sensation, not just dizziness alone. It has weak antinauseant effects but may not be as effective as Compazine for n/v. Phenergan (promethazine) is good.