Mirena IUD & weight gain/pregnancy?

I got my Mirena IUD in October 2017 and since then my periods have been getting lighter and lighter every month (which is what I wanted). In May and June my period came like normal with all my usual PMS/period symptoms (bloating, cramping, sore breasts) and light bleeding/spotting.

However I’ve gained a fair amount of weight in the past 2 months and it’s mostly in my stomach area. My period was last week and it definitely felt like a normal period but with super light bleeding. Is it possible I could be pregnant at all? Or I’m just gaining more weight than I’m used to? Anyone experience anything like this before?