What Causes Irregular Periods?

So, I haven't had my period in almost 4 months. I went to the ob/gyn 2 weeks ago. I saw a nurse practitioner and she said it is perfectly normal to not get your period while on the pill. I have had my period for about 7 years and have not once missed my period. She said if I still felt uncomfortable I could go off the pill and see if I got it. She said to wait 3 months then come back if I still didn't get it. Well, I still haven't gotten it (I know it is early) and my stomach has been sooo bloated the past month. I usually get bloated, but it goes down after a day or two. The bloat I have now has been there for weeks! I have been working out too and eating healthier so you would think it would go down. I am not comfortable waiting 3 months, so I am going to call and go back in. Oh I also took a blood test last month for pregnancy and it was negative. What do you all think about this?!