Camshaft position sensor location?

Okay, I am not mechanically inclined. My check engine light is on, it says cam shaft sensor, changed it twice still messed up, it revs itself when I first start it this will last up to five minutes. It misses bad when I change gears (stick shift) it makes a loud rattling noise when I first start it too. Also the RPM's goes down when I let off the gas like it wants to quit then runs back up when I hit the gas. I have had plugs and wires replaced also it only has 89,000 miles. I am at a loss and don't have the funds to keep dumping in it with no results. Do you have any ideas at all? Please help because it has shut off twice while I am driving.