Messed up period on Yaz

Patient: Hi, I have a question on birth control pills, I started taking Yaz 5 months ago and I took two packs before I got my period which was not long, and then I took another two packs and nothing and still have not received my period, is this normal, is my period gone now because of these pills, or just messed up? I hope you can give me some insight on this, after the first two months at the beginning I took a pregnancy test and it came back negative. Thanks for your help