Looks like you're using level_load for changing levels. That means every time you load a level it will be exactly in its initial state. If you want to avoid that you have to save the game when leaving the level and later on load that game back when your player reenters that level.
The following commands might help you:
http://www.conitec.net/beta/asave.htmhttp://www.conitec.net/beta/aload.htm
