Celsie,
Good for you. You are doing the right thing taking action now. Don't wait until after the 20th. You have visual proof that the job was offered to you and the only thing that has changed since he offered you the job is that he has found out that you are pregnant. And not in an underhand way. You were open and honest. Fight it and give him what he deserves.

I wish you all the best.
Debbie