Burning during sex?

I've had my IUD for a year now, and my last periods came two weeks apart (which is strange for me). It's been about two weeks since then, and last night I started cramping like my period is coming. My boyfriend and I had sex and after a while the entrance to my vagina started burning when he entered me? It's never happened before, and I wondered if the period thing had something to do with it as well. But has that happened to anyone else?

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