In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
Thanks for your question, and we implore Allah to guide us all to the best and to help us gain insight to understand the teachings of Islam.
Some Muslim scholars state that Muslim women are permitted to take medication to stop menses during Hajj in order for them to be able to perform all the rituals uninterrupted. The followers of this view state that the medication should be taken under the supervision of a reliable physician, and it should in no way harm the health of the woman. Other scholars state that it is not necessary to suppress the menses, maintaining that controlling the menstrual cycle for the sake of Hajj and `Umrah is not necessary.
Responding to the question, the Islamic Religious Council of Singapore states the following:
Thank you for your query. We commend your effort to seek the truth in the religion.
Menstruation is a natural process ordained by Allah, the Creator of human beings. Thus, there are certain wisdom, rationality, and benefits behind menstruation. Among them is the production of progesterone and other female hormones essential for the well-being of a woman. Suppressing these hormones may lead to certain undesirable side effects such as increased weight. Islam discourages inflicting harm on oneself and others. Thus, it is better to avoid taking contraceptives unless necessary. Controlling menstrual cycle for the sake of Hajj and `Umrah is not necessary.
`Umrah is not wajib. If it is ordained by Allah that a woman bleeds during her `Umrah, then she should accept it with an open heart. Allah knows what is best for His servants. And Allah knows what is in her heart. And, in sha' Allah, she would be rewarded for her good intention.
As for Hajj, it is not necessary to suppress the menses. Even the Prophet's wife `A'ishah (may Allah be pleased with her), bled during her Hajj with the Prophet. All activities of the Hajj, except Tawaf, can be perform by a menstruating woman. And this Tawf can be done anytime after the first tahallul (going out of ihram). Thus there is plenty of time for the woman to do her Tawaf.
But if she has taken the pills to suppress her periods, her acts of worship are still valid.
We hope that this reply answers your question. A good book that you can rely on is The Reliance of the Traveller translated by Nuh Ha Mim Keller, which can be found in many Muslim bookstores.
Allah Almighty knows best.