Hey, perfectly normal question, and if it weren't for the almighty period, none of us would be here. It smells that way because once it leaves the body it starts to break down (decompose) like all natural matter. You can always use scented pads, and carry most towelettes to stay fresh and clean. Change your protection often, especially on heavy days. Good luck sweety.
I suggest a vaginal douche when your period ends. It can be a commercially prepared one or you can prepare a quart of warm water with a cup of vinegar and place it into a douche container. The odor is not normal, so if the douche doesnt help, see your doctor
All of the answers are helpful! you may need to simply take extra care with hygiene. One thing to mention... If this odor occurs any other time , you need to see DR. it is called bacterial vaginosis. it Is not uncommon , but needs to be treated with antibiotics. it is not exclusively caused by having sex. it occurs for many other reasons .