95 Tbird, V8: Check Engine light & vibrations

Hi!

My Tbird has just over 100k miles and she's run like a dream so far. But yesterday when I started the car after work, I felt the entire car vibrating, especially when I stopped at lights. A few minutes after I started the car, the check engine light came on. This has never happened before. I went home and checked the oil and there was almost NO oil, even though I am positive I changed oil less than 3 months and 3k miles ago. So, right now we are getting the oil changed. Does anyone know what might be wrong?

Thanks and have a great day!

Valve guides come to mind.