Hi Sophia,
On days 25-28, what women take depends on their symptoms. Both estrogens and progesterone drop fast on day 25, and which one drops faster may vary from cycle to cycle. If you feel estrogen dominance (headaches or lower back pain, foggy thinking, low libido, depressed mood, bloated ankles) take a low dose of fenugreek, or, if you don't want prolactin, vitex agnus castus. If you have bad pre-menstrual syndrome, and feel easily irritated, take a low dose of a phyto-estrogen.
1) Many women with PCOS have estrogen dominance or androgen excess symptoms (oily skin or acne, shedding scalp hair, growing facial or body hair, upbeat mood, or even dominance, or aggression on provocation). But not every women who has PCOS has both estrogen dominance and androgen excess symptoms. Use the symptoms to determine if you do. Or google dr. Lee's hormone balance test.
2) Lowering phyto-estrogen doses on the 3rd and 4th week is a good idea. Phyto-progestin doses are lowest (zero for those without PCOS) on days 25-11. Phyto-estrogen doses are highest on days 9-11.
3) PCOS - fill out dr. Lee's test and see if you have estrogen dominance or progesterone deficiency or both. Then try if more progesterone helps. Some women use fenugreek or wild yam, some use a phyto-estrogen like fennel or turmeric or damiana, some use progesterone cream. You can also try vitex agnus castus, of course.
Your body lowers its own steroids production if the total of all sex hormones is too high. You grow best when estrogens are high and all the others are low, except if you have estrogen dominance. Then it helps to lower estrogens or to add something progestogenic. Which of the two will work best, follows from dr. Lee's test: if you have both estrogen dominance and excess estrogens, lower estrogens. If you have estrogen dominance and progesterone deficiency, or if you have only estrogen dominance, add progestogens.
Estradiol is made from testosterone. The reverse does not normally happen:
http://en.wikipedia.org/wiki/File:Steroidogenesis.svg