Key Drop Rate?

I know that 3 keys, which randomly dropped after a game are needed to forge hextech key. I opened 3 chests so far. First was given, Second key i earned from game, third key i bought cause i had chest but could not get a keys. Now I have 3 chests but haven't got single key since i opened second chest. So, how ridiculous is drop rate of keys? I think i haven't got single key in month, and played 3-5 games a days. Really? [zombie-brand-facepalm]