Is It Normal To Have Spotting While On Birth Control Pills?

I started birth control about 2 weeks ago because my periods were extremely irregular. I wouldn't have my period for longer than 40 days and they would last about two weeks. When I started the birth control I had not yet finished my period. I believe it was day 13. I'm about to start my third week of birth control and throughout these two weeks i've been spotting everyday. Is this normal?