What is causing my itching ?

Last week (about) I started getting itchy down there, and I’m pretty sure it’s not an STD. I got my period (which was 15 days late) and the last two days of it, when I itches when I first put the tampon in. It was more on the opening or the vagina. Today, when I’m off my period, I’ve been getting itchy all over again in diff spots on my vagina. Don’t have a smell or funky discharge and no pain whatsoever. What could it be?