Is it normal for me to have my period even if i am on an active pill on birth control. i just finished a course of antibiotics for tonsillitis.

No usually, but...: Breakthrough bleeding happens sometimes. Women can have occasional variation of their mucus discharge, some spotting between periods, a heavier or lighter period, a longer or shorter period, or a variation in color of period. Having one or two of these symptoms doesn’t necessarily mean there is a medical problem, but a call to one’s doctor is a good idea if bleeding is persistent or worrisome.