Period and Vacation

So my period has been very irregular lately. In June I had it for 2 weeks. I didnt get it at all in July and I have it this week. The problem is I have a vacation with my boyfriend Sept 3-13 and I didnt want to rely on norethisterone to delay my period for this trip because I didnt want to mess up my ovulation cycle either. Does anyone know if norethisterone effects ovulation cycles too?