Quick female lesson before I offer my suggestion.
The first part of your cycle (menses to ovulation) is when time variances usually occur (ie stress etc). You many ovulate on day 14 as a general rule, but have a stressful week - ovulation can be delayed. Ovulation does not always occur on day 14 as is commonly believed. (charting your temperature is a great way to know exactly when you ovulate.) The second part of the cycle (the Luteal Phase) is,
unless medically altered or pregnant, the part of the cycle that does not change. If it is 12 days, it will always be 12 days regardless of stress etc. The luteal phase is the time between ovulation and menses. Luteal phase defect is when the LP is less than 10 days - as is mine (makes it very difficult to get pregnant). But I don't ovulate until day 19 (or so) so I still appear to have a "normal" 28 day cycle. Using the following (b-6 and progesterone cream) I was able to add 3 days onto my LP, so it's not a huge difference, but 2 days may make the difference as far as not having "Aunt Flo" visit while on vacation... It usually takes 2 or 3 months of treatments to start seeing a change. If you are interested in trying this, I'd strongly suggest the book "Taking Charge of Your Fertility" by Toni Weschler. This is good for young and old alike!! (including gals who are not sexually active - BTW- YAY! to you!!

) I found a copy in my local library so I didn't have to pay for it.
The luteal phase has been successfully extended by many women with the following over the counter items:
The two main things that help to correct a luteal phase defect with over-the-counter remedies are vitamin B6 and progesterone cream. Vitamin B6 can be taken daily in dosages from 50 mg to 200 mg. Vitamin B6 is perfectly safe to take during pregnancy as well. Taking vitamin B6 every day during the entire month will help to lengthen the luteal phase as well as ease PMS and morning sickness.
A progesterone cream is usually targeted for menopausal women, however this cream is also useful in lengthening the luteal phase. A cream with natural progesterone works best. Be cautious of creams containing wild yam - because wild yam contains estrogen as well as progesterone. Use about 1/4 to 1/2 a teaspoon of progesterone cream spread on the inner arm, inner thigh, neck, and chest - alternating places - twice a day from ovulation to menstruation or until the 10th week of pregnancy. (Ask your doctor for advice before using the progesterone cream.)
Another safe supplement that can help lengthen your LP is Red Raspberry
(335 mg pure Rubus Idaeus twice a day) to strengthen the uterus, thus lengthen LP.
Feel free to PM me if you have more questions - I've been doing this (charting etc) for many many years and am glad to share with anyone who is curious.
Hope that helps a little bit!
Robin