Poor performance & fan on at all time... help?!

I have always taken care of my computer, completed the software updates whenever possible, but now I've noticed that my laptop performance is not as good as it used to be (jams several times a day), and the fan will not turn off, despite my efforts to cool off my notebook. I bought it in November 2011, it is barely 1.5 years old. Can anyone help me figure out why this is happening, or any tips on how to get the fan to stop? Thanks a lot! 🙂