Should periods be the same every month on birth control?

I am on my fourth period after starting junel fe 1.5/30. The first two months i spotted and the periods were heavy but by the third period it seemed like everything was evened out and it was even lighter than usual. I was very happy and expected them tk be like that from then on. But this period started a few hours early and has been heavier. I needed a tampon today and never ever needed one on the first day in the past, even before birth control. I'm scared that this period will be extremely heavy. Is it normal for periods to vary on birth control? I thought they were supposed to be almost exactly the same every time. My periods before were irregular but the flow was always the exact same every month. I am not sexually active so I am not pregnant. Why is my period different this time on the fourth month? I know the dose is right because I do not have any other side effects! Any advice would be appreciated!