My Pokemon Pearl game keeps freezing! Why?

My pokemon pearl game for the DS keeps freezing after EXACTLY every minute! I got it off eBay without a case so it maight be fake but I'm not sure. It was working about half an hour ago (Before I wrote this) and now it keeps freezing! It started when I found a wild abra east from Jubilife city. My Pokemon is 1 Chimchar called Chip lv.12. Please help!!