Telling a job your pregnant?! Neccessary or not?

Jae • Love.Peace.Happiness.

Im looking for a 2nd,part time job, to save a bit. I have an interview next week and I am wondering if I should tell her im expecting. Im 3 months,so it is not obvious.

Do I Have to tell her right away? I feel like if I do, that may sway jobs away from me,though I know thats against the law...but im sure places discriminate anyways.

Do I not say it during the interview? But then what if I got the job? When do you tell your job? After a week, a month?

Any advice!!? Thank you