Why does the side of my left hurt?

I'm 14, turning 15 in about two months. I noticed about an hour ago that the left side of my left hurts. It's also not as squishy as my other one... I think I'm supposed to have my period in a couple of days since last month it came on the 9th. Why does it hurt? My mom's a doctor and I asked her about it, she says it's probably normal...