Heavier Flow Than Usual?

Chey
Okay! So I'm on birth control (nexplanon) and it's made my periods very light with some spotting in between periods. Like I've never had to really use an actual pad, I've been okay with liners only when I'm on what would be my period. I started my period this Sunday and it's pretty early. My flow has been really heavy, and heavy meaning having to change my pad every 3 hours because of the flow being a little too much. It's been like this since it started and I'm just really confused and a little concerned. 
It could be nothing, but I just wanted to get some opinions?