Have you ever been to Jamaica? Take a deep breath and prepare to relax. Take a book, go to the beach. You may want to take a few staples for your diet, peanut butter and jelly, crackers. You never know what you are craving that you can't get easily while you are there.
Have you checked the weather while you will be there? I would plan for chilly weather clothing too just in case.
The "taxi" ride to the resort (I hope it is all inclusive) will take over an hour to make. Jamaican's drive like a bat out of hell and on the opposite side of the road than you are accustomed to. There may be stops involved along the way, it is a bumpy, barely there road with cows, dogs and goats sometimes milling about. The scenery on your way to Negril is beautiful though. This might be the worst part of the trip for you but now it doesn't have to be because you have been warned.
The culture shock alone of going into a third world country is stunning. The locals all rely on tourists for their economy and are not shy about asking for it from you directly. I didn't like being touched that much by strangers when I have visited there. We usually stay at Sam Sara in Negril. My family goes for three weeks every year.
Don't forget you will have to exchange money. The airport has a place to do this but sometimes you can get a better rate at a local place for currency exchange.
I was in a wedding in Negril in 1995. The water workers went on strike in the middle of my shower before the wedding. We laugh about it now.
To calm your fears, I don't know how to help you with that. New mothers and even those of us with an older child, it is still scary to be going to a new place with your baby.
The food is wonderful, the locals are interesting, the music is fun.
I hope you have a fantastic time and take lots of pictures.
Good Luck!