An American tourist once asked a Jerusalem rabbi how religious Israelis succeed in having such large families? The rabbi answered, "It's because Shepherd's Purse grows wild by the roadside all over the Land of Israel."
Lately, I've had numerous letters from women that complain of lengthy menstrual cycles that leave them few days of purity and reduce their chances of pregnancy.
Rebbe Nachman says there's no such thing as despair. Save your money, don't run to the gynecologist, and don't fill yourself with pills. There's an easier, more natural way to become clean on the 5th day, so with hefsek tahara and 7 clean days, the unpure period is reduced to 12 days. With ritual immesion in the mikva after sundown of the 12th day, a woman's chances for pregnancy are highest, since for many women, ovulation is on the 13th day of the cycle.
Here's all you need to do (I learned this remedy from the great Rabbi Yisroel Yaacov Fisher ob"m of the Eda Haredis in Jerusalem): Gather 5 or 6 young green leaves from a shepherd's purse plant that grows all over the place here, at roadsides and on empty lots. If you live outside of Israel, ask your local herb specialist for the leaves. Wash them off in cold water and make sure they have no bugs in them. Then, boil them in a small tea kettle with water, letting the herb tea brew for about 5 minutes. It may be a bit bitter, so sweeten the tea with a teaspoon of honey. Drink a glass of this tea on the mornings of the 3rd, 4th, and 5th day of the menstrual period. Before sundown of the 5th day, you'll hopefully be clean as a whistle, so you can begin counting the 7 clean days and therefore immerse G-d willing at the end of the 12th day of the cycle.
This remedy has worked for many families in Israel. Hopefully, it will work for you too.