I believe less than 10 days is considered a short LP. Your body needs at least that amount of time for the lining to be in the correct alignment for implantation.

I'm breastfeeding and TTC#2. Breastfeeding is all about the hormone prolactin, which suppresses estrogen and progesterone production, and increases FSH. It is common while breastfeeding to have delayed ovulation and a short LP.

One herbal treatment option is to use Vitex, which adjusts the amount of prolactin in your system.

I've read that too much stress can also elevate the prolactin level, as can too much sex (go figure). Trying to reduce the amount of stress on one's body is a multi-faceted endeavor - including significant diet and lifestyle changes.

Another approach is to try acupuncture/TCM, which can adjust your hormone levels, but TCM will also require diet and lifestyle changes.

Someone I know had short cycles and she opted to try Clomid and that worked for her. She made no lifestyle changes, but the she had a rough time while she was pg with hyperemesis gravidarum and the baby had intrauterine growth restriction and had to be born early by c/s. I wonder if she tried a different, more healing approach for her body if she wouldn't have had a better, healthier time during pg.

Menstrual Irregularities

Here's a page which illustrates/explains different types of menstrual irregularities:

http://www.femalehealthmadesimple.com/FileTwelveFinal.html

"Any woman of childbearing age who has missed more than two consecutive periods -- but was not pregnant -- needs to investigate it and possibly have her period induced. Preventing the development of hyperplasia is the reason."
From: Endometrial Hyperplasia, WebMD

"Excessive estrogen stimulation can lead to significant increases in uterine lining thickness. The tissue becomes hyperplastic or atypically hyperplastic . It may become cancerous."

(and)

"Inadequate ovulation may cause excessive, irregular, or frequent menses recurring less than every 3 weeks. Inadequate ovulation leads to an excess of estrogen, which stimulates growth of the menstrual lining, and a decreased level of progesterone - which normally would be present in levels that would adequately thin the menstrual lining and prevent excess or irregular bleeding."
From: Dr Decker, Heavy Menstrual Cycles Management Options

"We like to see a lining of at least 8mm in thickness when measured by ultrasound at the time of maximal thickness during the cycle (see above ultrasound images of an 11.5 mm lining). There is some ongoing debate as to "how thin is too thin", as well as to "how thick is too thick". In general, 8-13 mm is good, less than 6 is potentially a problem, and greater than 15 or so could possibly reduce chances for a successful pregnancy."
From: Uterine problems causing infertility or miscarriage

Information about the endometrial lining and menstruation.

There is a substance produced in the uterus which is supposed to help prevent clots from forming, it is called fibrinolysin. When the blood flows too quickly (profusely) the anti-clotting fibrinolysins can't keep up and clots form. Heavy bleeding is called menorrhagia.

"Blood clots or flooding are indications of heavy loss. Normally the blood lost from the vessels in the lining of the womb forms small clots and this tends to reduce the flow. The small blood clots within the uterus are broken down by chemicals called fibrinolysins and the normal menstrual loss should be a fluid. When the bleeding is heavy, the blood is extruded too quickly for it to clot within the uterus. In this situation, the blood clots in the vagina and the menstrual flow includes blood clots. Whilst menstruation is inevitably an inconvenience, it should not result in limitation of social activity."
http://askwaltstollmd.com/archives/menstruati/95779.html#95952
(This doctor had his licensed revoked but the information seems valid so I included it, you will see mention of it if you scroll down through the previous link so I thought I would link to this page FYI: (http://askwaltstollmd.com/faq.html)

Check out these two interesting pages with detailed descriptions and diagrams of how the endometrium forms each month, for your reference:

NORMAL MENSTRUATION

THE ENDOMETRIUM

For more information search with these key words in different
combinations (such as "endometrium anti-clotting"):

menorrhagia, endometrium, fibrinolysin, anti-clotting