Going to try ibuprofen

So I have extremely bad period cramps. I have had to come back home from college and miss important classes because of this. My periods are otherwise regular. I want to try taking pain killers and many suggested ibuprofen. So how should I take it ? How many grams? When should I start? On the day of period? How long will it's affect last And most importantly, it's side effects in long term use? I need it only on first day, I am ok from second day onwards. But on first day just the initial 1-3 hours are unbearable. Pls guide.