Three week cycle anyone?

T

Can someone help me understand. We’ve been ttc #2 for the last 15 cycles. I originally used to have 27-28 day cycle. We had a MMC in March and ever since my cycles are approx 23-24 days. This Cycle went down to only 21 days?! I started spotting today at 21 days with bad cramps. How do I know which phase of my cycle is short? I got a peak ovulation on cycle day 9. So is my fertile window when I’m finishing my period? Seems so odd. I’m so frustrated.