Weird cycle

KP
I normally have 21-23 day cycle. Last month I had tiny bit of brown spotting on day 20, then it went away. I got excited, thinking implantation bleeding (happened with my son, who is 5). Tested a few days later - nothing. Tested every day maniacally - nothing. Period finally came on day 30 with heavy flow, clots, cramps, terrible pain. What is this all about?