What is the first step I should do contact a lawyer or who? Do I have a case?

I am almost 9 months pregnant. My boss gave me and only me a evaluation yesterday it was poor. Said that I will be re-evaluated in 30 days. if not better then I can receive disiplinary action up to and including termination. I have a feeling she wants to get rid of me before I go out on maternity leave. I have been employed there for over 1 year 3 months. I am full time with benefits. Today she offered my Recruiter position to a hourly temp employee that has been working there for 1 year on and off. effective July 1, 2010. there is another office support staff person employed there for over 4 years and she has never ever gotten a evaluation in all of her 4 years employed with the company. I have other email documents showing discrimination as well.