Took plan b got period can I start birth control pills

Hello I took the next choice aka plan b recently I have taken the next choice before and a day or so after taking it I started bleeding for two days. I was unsure about taking it this time because I was supposed to get my period anyday but didn't want to risk it any longer and took the next choice. The day after I started bleeding a little then had bad cramps and have been bleeding for four days. Is this my period it seems like it I'm sure plan b made me bleed but this seems like my period more than my experience with plan b last time. I was also wondering can I start the birth control pills once the bleeding stops? This really seems to be my period strange enough. I need advice.. Thanks.