On the shot - weird cramps

Aimee • 18, with the love of my life💍 and I'm a musician 🎶💞
So I'm newly on the shot and I haven't had any spotting or anything like the doctor said I might have - she even said I might not get a period at all! I'm 12 days from my next period supposedly but I've been getting weird period cramps all afternoon. Is this a side effect of the shot or is my period just coming earlier?