Maternity leave help

So I was offered a job in November. I started January 22nd and was 6.5 weeks pregnant at that point. Now I am almost 9 weeks. I work for a large corporation with great benefits. However, legally they do not owe me FMLA and I’m worried about telling my boss about the pregnancy before my 90 day probation period. But by then I’ll be 6 months pregnant and there’s no way he wouldn’t know! What should I do? What are my legal rights?