The oil light in my car is blinking erraticallly and I don't know why.?

I drive a 96 mazda 626. I noticed yesterday that my oil light is blinking on and off really erratically. Usually if one of my warning lights comes on it stays on and doesn't ever blink. My engine is also smoky after I've been driving it a while. I had my oil changed about two weeks ago. I checked the oil yesterday and the level was fine. Could the oil still be the problem? Is there some valve the oil changers didn't close properly perhaps? Also, I had my water pump belt and my power steering belt replaced last week. Could that be the problem?