Mirena and Stomach Probs

I’m about 10 months into Mirena. Once a month lately for a couple of days I’ve been getting cramping and my stomach feels off (gassy, not much of an appetite). I’ve even had some brown discharge with some red mixed in. I freak myself out every time thinking I’m pregnant, but I just got my placement checked at the beginning of this month and they said I’m good. Does anyone else experience this on Mirena or hormonal IUD? Do you think this is just when my period would be if I was still getting it?