I took plan b pill on sept 21st , a week later i got my period. on oct 10th i took it for the third time . i have heard you should only take it twice?

My suggestion is not: to rely on continued use of Plan B, but to get on something type of more consistent birth control and not rely on episode and periodic use of Plan B. If you are having sex more than once or twice a month, it is probably worth your peace of mind to take something where you are continually protected. A doctor or family planning clinic can discuss options with you.