upset at my co worker congratulating me and this is why. 12 weeks pregnant

So am 12 weeks pregnant and I have not told any of my co workers. I got to work today and in the med room taking report from the out going nurse .  And I hear someone yelling out my name outside. I thought it was an emergency. So I went out and it was a CNA. She goes congrats . And am like for what ? And she said you think i don't know you pregnant ? And am like first of all I have told you anything for you to congratulate me. I just hate noisy people who want to know everyone's business. I don't plan on telling anyone at work about my pregnancy. The only people am telling is HR so can I get info about meternity leave. Was she right for congratulating me while I have not told  her anything. Plus am not even showing yet. How do I deal with noisy crazy workers without being mean?? Any advise ???