hi oceandeep, I am no expert but short cycle can also be due to defect luteal phase, i.e not enough progesterone after ovulation, causing AF to arrive earlier.
Typically a luteal phase should be around 14days. For instance, you might have O on CD14/15, but your luteal phase only lasted for 8-9 days. Progesterone is important for the uterus lining to thicken so as to prepared the fertilised egg for implantation. If the lining is not properly formed, it will affect implantation, causing very early miscarriage, or chemical pregnancy.
Which is why some gynae introduce progesterone in forms of pills or jab during very early pregnancy should there be suspected case of low progesterone level, to minimise risk of miscarriage. Symptoms of low progesterone include short cycle, low BBT after ovulation, irregular periods, very bad PMS symptoms, etc...
You may find out more information about luteal phase defect online. Hope this information helps.