There are many reasons you might miss a period. Simple things such as stress or exercising too much can cause a missed period and many girls are irregular during the first few years of menstruating. But if you've missed a few periods, be sure to see your healthcare provider.
Courts usually find probable cause when there is a reasonable basis for believing that a crime may have been committed (for an arrest) or when evidence of the crime is present in the place to be searched (for a search).
Probable cause means a compelling reason to believe that you may have committed a crime. Criminal defense attorneys have a nuanced understanding of probable cause as it is defined within your jurisdiction and may be able to present a challenge to the officers reasoning in court.