Period,birth control, pregnant?

ok so i started taking the pill 2 months ago. last month my period was supper heavy but this month its lite. is that normal does the pill make periods lighter or could i be prego. we always use protection but a couple of days ago the condom slipped off. i took an emergency contraption pill tho. but idk ive gained weight and im worried please help! im worried abt being prego cuz i know you can have spotting while pregnant.. help..