What Causes Positive Pregnancy Test Results Inspite Of Menstruation?

Hi doc i gave my wife mifty kit because her periods not on time and we check via pregnency kit and that was positive result then i gave her she took all 3 dose and she got periods only for 2 days but still she is feeling vomitish and we check again during period time its still showing positive. Should we ha e to wait to finish periods or i have to consult doctor?