I Have Been Having Irregular Cycles And Today I Went

I have been having irregular cycles and today I went to the gynocologist & he proscribe me with birth control ( Necon 1/35 ) and I have no refills I was wondering if its just to get it started & I don't have to take no more after the 1st pack . or do I have to take it constantly . I'm confused and is it best to start on a Sunday sense today is Wednesday.