I have decided to take a trip to St. Kitts. I have searched for connected flights from Jamaica to St. Kitts, however the hours were too long and I do not want to lay over. I have decided to purchase two separate electronic tickets, one from Jamaica to Antigua, then the other from Antigua to St. Kitts. Would I be in transit when I land in Antigua, since it's not a connecting flight? Would I still need to go through immigration and customs? What am I expected to do?
I have not been through the new terminal at ANU and cannot give a firsthand account; however, I do not believe it has an airside transit area, and since you are flying on separate tickets, that point is probably irrelevant.
Once you disembark your incoming flight, you will proceed to immigration and customs for processing. Reports are that the signage is unclear, so look carefully for the lines for transit passengers. Jamaican citizens are exempt from entry visas to Antigua & Barbuda, so as long as your passport is in order and you have evidence of your onward ticket, I would not be overly concerned about these formalities.
Once you are processed by immigration and customs, you can then proceed to the desk (LIAT, I presume?) to check in for your connection to SKB.
All the usual caveats of flying on separate tickets apply. If your inbound flight is delayed, or if it takes an unusually long time to be processed, you will not have legal recourse to be reaccommodated for your onward flight— and ANU, even in the new terminal, has a reputation for slow processing. Be sure to leave ample time.