Birth control and still no period

I'm on birth control and I'm not always on time taking pill but I do take it.Rite now I'm in the 4th week so that means I should be on my period .funny thing is I missed my hole cycle and now in my fertile stage. Why do I do ? Should I take a test? Should I finish my birth control and maybe hopefully I will get a period at the end of my four weeks. I'm confused ....!!!!!!