new to birth control; confused.

Mary • Confidence and Kindness.💓
I'm 16 years old. And a type 1 diabetic. I recently started taking the Birth Control known as "Sprintec" - First time; first experience. I was nearly done at week 3 of the 28 day pack, but just on Monday of that 3rd week, I started my period again? - still having 5 left before the fertile 4th week section. I did not miss any pills. I've been precise. Any ideas..?