Will crank but won't start sometimes

After a bunch of rain last week and not driving the car for a few days (not wanting to put tire tracks in the wet grass) I went to start the car. It would crank but not start. I checked the spark plugs to make sure there was spark and there was. Two days latter I went out to hook up jumper cables just to see if the battery didn't have enough power and decided to try starting the car again. This time it started right up on the first try. I shut off the engine and restarted with no problems then took the car to run errands and drove for over an hour. The next morning I went out to take the car to work and it would not start again. It would crank but would not start. Then that afternoon tried it again and ti started right up repeatedly.

A friend suggested checking the fuel pump relay but cannot find the relay based on my Chilton's manual for the car.

Is this a problem with the fuel pump relay and if so where is the fuel pump relay on a 1999 Altima SE?

Thanks for any help.