Pregnancy discrimination, Arizona

Yesterday, at 33 weeks pregnant and after over 19 months with my company, my employer brought me into his office and terminated my employment effective immediately. He stated that he was going to take my position (Manager, HR) in another direction and hire someone with 5-10 years experience. In doing so, he offered me a very small severence package (3 weeks paid and 3 weeks half pay plus medical through May) if I were to sign a Mutual and General Release Agreement. They tried to force me to sign it site on scene, but I didn't and have retained a copy to sign if I feel that the agreement is fair. The monies offered would not even get me to my due date, and at this point, how employable is an 8 month pregnant woman?

Since then, I have contacted the one other person in our small company's history (too small to qualify for FMLA) who was pregnant when employed. She was "laid off" two weeks upon returning from her maternity leave. She was offered a small severance, but was not forced to sign a release agreement as a contingency.

Without getting into any details, I have feared for my job since I notified my employers of my pregnancy. On August 16th, I received a title promotion and a 23% raise followed by a very strong performance review in September. After I notified my employer of my pregnancy, his attitude towards me changed more and more negatively, culminating in my termination yesterday.

Do I have a case? Do I have grounds to negotiate the severence they offered?