Any ideas of why it smells weird down there?

I’m at a loss because I have such an odd smell coming out of my lady parts. I already went to a gyno. They did the swab test, blood test, everything! I came out in the clear and there’s no infection, no disease, nothing. However, when I’m on my period, I get such a nasty smell down there & it’s not a fishy smell. It smells like my blood is rotting or something. They did tell me it could just be a natural thing but i feel so gross and ashamed ): what can I do to fix this?