irregular period?

so the past couple months my period has been a week or so late and I am sexually active with my boyfriend. Also, one time I had my period and then 2 weeks later I bled for about 2 days and then 2 weeks after that I had my period. and after that situation I have had a couple periods, but I still am late. I used to never ever be late, and now I'm late almost all the time, such as right now I am 4 days late.