What is the cause for my period to have such a bad stench?

Any type of foul odor means that you have an infection. I would make an appointment with your doctor to have a swab test done to determine the type of infection, so the appropriate treatment can be given. Make sure you eat a balanced diet, and drinking acidophilus milk or eating yogurt that contains live Lactobacillus organisms can also be helpful in keeping a balance. Cotton underwear is also helpful in preventing moisture from developing. Make sure after going to the bathroom that you wipe from front to back. Avoid use of any types of feminine sprays, talcs etc as they can also disrupt the normal balance. Also avoid any type of scented toilet paper. Eating yogurt daily is also helpful in keeping a balance.