Changing bc?

been on Ganvai bc for year when I went to pick up my pills the pharmacy give me Niki I asked why and they basically said Ganvai was no longer available and that this other pill was the same thing and it s just under a different name but is the same thing. I m was worried that it may change my period as my period as always been very good on the old bc I also was scared that it will not be effective right away I called my doctor and the nurse that works with her said that it should not cause any new affects and should be affective right away bc its " the same thing" I still worry about Wonder if anyone has had experience with this and can hel