You should definately be looking at something out of Florida for a 4/5 day cruise, usually the Bahamas. Most of the Southern Caribbean itinaries leave from San Juan and its a long flight and those are usually for 7 days. Western itinaries are to Cozumel, Grand Cayman, the keys. On the Eastern you cruise as far as St. Thomas and visit a few islands there and then back to Florida. You can find quite a few shorter ones leaving from Florida.
You may want to post in the "bargain finder" here at Cruisemates. Once you post there, you should get e-mails from travel agents with what they may have for the time you want to go. Its worth a try, good luck and congrats on the upcoming wedding and honeymoon!
Tuesday Chat Host
Personally, I find the southern (eastern, not aruba/curacao) to be the prettiest. The islands are volcanic, with some reaching nearly a mile in height. With this height, they interrupt the wind flow and therefore get a lot of rain on the mountains which make for beautiful waterfalls and rainforests ala Hawaii. Some of the prettiest islands I've been to are: Dominica, Guadalope,St. Lucia, Martinique, Grenada. The eastern and western itineraries seem to hit more coral/desert islands that don't have the altitude necessary to generate rainforests.
However, most of the southern routes are 7 day routes, not 5. IF you only have 5 days, I think RCCL has something out of San Juan on the Nordic Empress that hits the US Virgin Islands. They are nice too with heights to about 1500 feet, not impoverished, and have nice beaches and snorkelling.