Read your pamphlet.

Girls. I'm sorry but there are so many girls on here who clearly aren't reading the medical information that comes with their medication. Before you took your first ever pill you should have read the leaflet to know about side effects, when you're protected and what effects the protection rate of your pill- things like some antibiotics etc... 
Can you all please read your pamphlet if you haven't already. I suggest reading it at least twice a year to remind yourself as well. 
If you've thrown out the paper, Google your pill and the information will be there.