These are the main reasons why the period blood smells:
PH balance – the levels of pH raise during the period, making the blood less acidic, resulting in bacteria growth down there and eventually bad smell.
Bacteria – the chances of present fungus and bacteria in the uterus lining are high during the period. The uterus lining sheds during this process, resulting in smell in the blood. If the blood stays longer in the uterus, the chances that it will smell stronger are higher.
Moisture retention – the moisture gets retained in the vagina during the period and it can sometimes cause fungal infections. This provides fishy smell near the vaginal area, adding to the bad odor.
Air blockage in sanitary pads and tampons – if there is a constant blockage of air in the sanitary napkins and tampons then there will be a bad odor.
Douche – in many cases a quick shower of water to remove the foul smell has not been proved to be a healthy option.
You should eat, exercise, and relax during these days, and before you know, you will be free as a bird for a whole month.