Nothing in the law says they have to put anything in your file before you are fired. Nothing in the law requires them to write you up before you are fired. Nothing in the law prohibits them from firing you without warning. And frankly, I'd have fired you after about the third accident; I'd never have let you get anywhere near seven without firing you. They were much nicer to you than I'd have been. It is perfectly legal and entirely understandable to fire you for that many accidents.
That being said, the timing of your termination is suspicious. Since they have a valid, non-discriminatory, LEGAL reason to fire you, a wrongful term claim is not going to be anything like a slam dunk. But if you think you were fired because of your pregnancy, the window for that closes at 180 days after your termination; 300 days if you filed with the state. If you're claiming a FMLA violation, I believe the SOL is two years; three if the violation is found to be willful.
How long ago did this happen?