Aiyoh, sayang, pain that's been going on since yesterday needs a doctor's check, please go see your GP or go to the clinic today, okay? Especially since it's on one side like that, better safe than sorry lah. I know it's worrying when something feels off down there, but I really can't say what it is from here, could be so many things, and you need someone to actually examine you. One of my mum friends had similar cramping and turned out to be nothing serious, but she still went straightaway because that's the right thing to do. Don't wait around, just go get it checked out, yeah? Let us know you're okay!