possible trigger: miscarriage or period?

Hello all, 
I gave birth to my daughter 2 years ago and have been in the pill since. The pill thinned out my period so much to where I wasn’t even having one any more so haven’t had any bleeding since way before getting pregnant with my daughter almost three years ago now. 
So, yesterday morning I woke up to light-medium bleeding. I called my doc and they said it is possible to still have 2-3 periods a year even if the pill has thinned them out to where they are not regular or even gone. Today it has gotten much heavier and I’m switching out my menstrual cup almost every hour with it almost full each time (it holds 4oz)
The doc assured me if it gets heavier to call them again but other than that seems normal. Well I know I have read on here before that during miscarriage you may still text positive for pregnancy so I was wondering if anyone has experience like that they would be willing to share? I have always taken my pill religiously, never miss a day. I just thought it was so strange for this to come on out of nowhere, and I am also still breastfeeding if that means anything. I took a test and I might be crazy but I see the most faint hint of a line. Any information would be very very appreciated. 
Thank you