Pain below belly button?

So I've had the mirena since October of 2013 for heavy bleeding and I've loved it. I got my mirena almost two years before becoming sexually active. I recently started having periods again (already talked to my gyno-says it's normal) but yesterday and today I have had really weird pain it's not severe just uncomfortable, below my belly button. I feel it constantly but it's worse when I'm trying to go to the bathroom. I'm due to start my period in 4 days.  I checked my strings and they feel normal. Should I be concerned about my mirena or could it be a bladder issue? Or because my period is due to start? Any ideas would help immensely.  Thank you 💖