just getting off birth control & my period is confusing me.

I started my period almost as soon as I went of birth control (December 14th). It was heavy, lasted about 5 days and then there were three days where I had sex with my husband. And on the third day, my period came back! This time it lasted only 3 days but was heavy like an actual period. I'm sure my body is just regulating after getting off the pill....and I put both periods into the calendar and I just can't tell if my percentages are still accurate? I am trying to avoid pregnancy as of now...HELP!