Birth control

I just started birth control due to bad period symptoms and the pharmacist said to take the first birth control pill on the first day of my period, so I did that. Now I'm on my 16th period day and according to my birth control pills I'm getting my period in 5 days! I'm bleeding very very little but my uterine lining is shedding and it almost hurts when it does and I'm only have period cramps now. Is this normal? Should I be concerned? What was it like when you guys started birth control?