Shortening cycles

Since I had my first at 37, I had to be put on birth control to start my period back up.  It did, and within a few months, I went back off of the pill and have stayed pretty regular (33-35 days).  Until the last 3 months, which have been 22-25 days.  I'm completely confused on my fertile days because they still have me on a 35 day cycle.  And I'm terrified because I will be 40 in May.  I'm running against the clock.