bi-monthly periods?

So up until may I was a college athlete it made my periods the most regular they've ever been (within in a few day of each other month) I stopped playing tennis in June , I missed a period in June, got one the 2nd week of July, skipped August, and got one the 2nd week of September. My periods have always been irregular but normally are every month. Any one else have this? What do u think?