What Causes Brown Discharge During Periods?

Hi, i'm feeling a ton of pressure right above my lady part. I don't know if its a cramp or not i'm not pregnant because i'm on my period at the moment. I was before started my period having brown discharge i believe it be just dried blood. I'm sexually active and on birth control. The pain is sharp, when i sit down it doesn't hurt as much but if i lay down the pain is increased more. Should i be worried? Or is it just cramps?