My period this month has a bad odor could it be the multivitamins i've been taking since last month?

No. Prob other: Taking a Multivitamin is a great idea. Bad odor with a cycle could be a vaginal infection. the most likely is one called Bacterial vaginosis, and is common in sexually active women (even non-sex active). It requires a MD exam and medication. There are other possible causes that need eval as well. Douching is NOT recommended by any physician group- so don't do that! Hope you feel better.