Am I over reacting?what would you do??

Am sooo offended right now,i just when to Walt Mar to buy some pregnancy test,i got 5 of them,i was with my friend,and the cashier look at the test and look at us and started cracking up,i look at her confused and she said, What??your not sure if your pregnant??and keep on lol in my face i didn't answer her,and she asked again is it for you or for her?then i said,it's non of your business,she keeps hahaha ,and then i give here the look,she was trying not to lough but she was doing it like making fun,iwas sooo mad i walked away as soon as i could i didn't want any problems,am i over reacting?maybe am just to sensitive when it's about this pregnancy thing.