Next and previous button cannot work well

my program is i can choose several movie to load and the movies are save in an array…
For example:
i choose movie 1 , 2 and 3.
Movie 1 was loaded. After i click 'next 'button, movie 2 will be show .Beside that,if i click ‘previous’ button, movie 1 will be show.
i facing a problem that my previous button is not back to my previous loaded movie but is trace my choices in arrays backward.
The next problem is, my first movie load to the second movie load will be a bit lagging. but the rest 1 is ok…
i can’t solve this problem…please help…