Hi unrulyjulie. I am on Cerazette and have been for years. When I first started taking it, my periods were on and off for a long time, i'd say a good 4 -5 months. I hated it and thought that it wasn't working, then after that time, they settled down and I didn't have anything atall for a good couple of years. Recently I got a period, however, I believe this to be because I stopped taking my pill regulary (as Im not in a relationship so didnt really need it), anyways, as soon as i started taking it again, I am back to having no periods atall. Love it! I'd say stick with it. it just takes time for your body to get used to it.
I hope this helps.