1997 Grand Am engine problem

This past weekend a clicking started under the hood (almost as though the oil was low). After checking the oil levels I did add some since it was at the minimum line. The clicking continued for a bit then stoped. I drove some, then when I stopped and restarted the car the clicking resumed. Then something new: the engine lost about 50% of it's power during acceleration. I've listened to try to determine where the sound originates and it seems loudest directly over the engine. Also when checking the oil there is a greasy buildup on the bottom of the cap that is like a yellow/brown grease. It will idle fine but with clicking. I'm a poor college student trying to determine the problem before taking it to a shop. Please help give me some ideas.