How would you deal with mother-induced paranoia?

My mother is kind of a paranoid person. I’m not clinical here, I just mean she gets really really worried about a lot of little things and tends to blow them way out of proportion. By this I mean she freaks out when I don’t use the club in my car and I’m parked in a locked lot that has a security guard on duty all the time and I’m often parked next to lexus’ and mercedes’. there are a lot of examples if this kind of reaction but it’s the latest one that is scaring me the most. I’ve been sick since last Sunday and throwing up on and off. My mother is convinced that I am pregnant and keeps pestering me to go into planned parenthood to get a pregnancy test done. When I told her that the first time I got sick was right after my period and before my boyfriend and I had had vaginal intercourse this month, she just said it could have been a false period. it wasn’t until today when I broke down on the phone in tears telling to stop telling me that she thinks I’m pregnant because it is scaring the hell out of me that she apologized (I’m 20, btw).

My question is, how do I deal with this kind of reaction in the future? For the little stuff like using the club, I usually just ignore her advice or only follow it when she’s around, but for the big stuff like this, I’m not sure how to handle it and I’m pretty sure I can only break down in tears once or twice before she starts saying this stuff anyway.