I had a period at the beginning of September and am now having another period at the end too, between the two periods it was 22 days, 3 days shorter than the last couple of cycles which have been 26 days. According to NHS ovulation calculator there are going to be two fertile windows one at the beginning of October and once heading towards the end of October. I've been using clear blue ovulation tests and it says start testing on day 6 which will be wed. Just wondering is this possible to have two fertile windows in one month? Can you test again for ovulation?.