What Causes Light Spotting During Periods While Having Nuvaring?

Hello. I have been using the nevaring for about 10 months my periods were very normal for the first few months but these past three months it has been extremely light almost like a spotting i m worried I might be pregnant via doctor told me as long as there s blood when I m supposed to start my period no matter how heavy or light it is I don t have to worry please help me