Commonly known by its trade name, Clomid, this is the first line medication very commonly used in fertility treatment. What Clomiphene does is to increase the number of eggs released from the ovary in women who are already ovulating. For those with irregular or no ovulation Clomiphene forces the ovary to develop and release the egg. In either situation, your menstrual cycle becomes regular, ovulation becomes predictable and your fertility increases.
However it also has side effects which can reduce its effects. The most common is mood swings and occassional blurring of vision. These however are of short duration and can be tolerated.
A more serious side effect is that it can cause the uterus lining to become thin. This of course means that even if an embryo forms, it will not be able to implant successfully in the uterus. So if you are taking Clomiphene and your periods become lighter, it may signify that your uterus lining is being affected by this negative effect. And consequently, there is no point in continuing with the clomiphene. Best to change to other medicines which will make you ovulate without affecting uterine quality.