Im on my period and pregnant

It happens to me before, the first time I ever got pregnant when I was 18 it was supose to be a joke on the nurse, but it turn out to be a joke on me, my friends and I was going to do a fake pregnancy test because we didn't want to stay in class so we all decided to go to the nurse office, we where 6 girls that did the pregnancy test and 3 came back positive, I was the 3rd, so the nurse ask me have you seen your period yet and I said no that my period usually comes the end of the month, which the month had not ended, so she told me the test could've been wrong that I should wait till the end of the month, ok before the month could over my period came on time and regular I was so excited that my period came, so I told my nurse, just to find out I was still pregnant while on my period. Has it happen to anyone?