What would be wrong with the blower fan on my 97 Plymouth Voyager?

I've been having problems with the fan for a while now. At first, it just made a noise whenever it came on, but as time ped, the fan got slower and slower, and now it doesn't even sound like it comes on whenever I turn it on. If it does come on, I get a weak airflow and there's a loud noise (more of a rough noise, not hi-pitched at all) while it is on and after some time pes, it completely shuts down. When it is on but not blowing, I do get some air from it (hot/cold, depending on what it is set for). I'm not sure what it would be, can I get some advice on it?