Period changes after BC?

Is this normal? My periods before usually took 4 weeks to 6 weeks to usually occur but lately my last 4 periods (4 months on birth control) my periods have been 3 weeks apart, then 2 weeks, then 3 weeks back to 2 weeks but my periods have been really light. My recent one lasted for 3 days (almost barely any blood to tell i was on my period), the one before that started for one day then stopped, started again then stopped then carried out onto 9 days. I'm not sure, I'm used to long extremely painful,emotional periods and extremely heavy flow. I know that my period will change with BC but with how extremely light it's been i just feel really off

>=< EDIT My most recent period was 3 days, stopped for one day, and when i woke up this morning i was bleeding again but as usual extremely light (if it helps the day my period started i had sex, and yesterday i had sex. I know sex can effect your periods. But my period in general came weeks early)