cramping can be caused by a number of things. Low Potassium is only one cause, some will excrete more potassium than others during intense training I had to get prescription dose K that I would take every other day and pretty much cured cramping (700mg tabs). Other causes can be low sodium intake, calcium-magnesium low. How do you figure it out? Try them all one at a time and see what works. It is very rarely low sodium as we get enough in our daily diet quite easily. Another case happens when you are having extreme changes in diet. Na and K like to travel hand in hand. sodium restrictive diets can cause a crash in potassium levels, followed with excessive water retention and then more cramping. Without knowing exactly what you are doing, hard to offer a suggestion. Were you doing anything different right before this, as in days before? I know what you are going through, I used to get pec cramps just brushing my teeth. Do you drink enough water?
From what you're saying it could be a sudden change in diet, well I think as of tomorrow it's my 11th week dieting (brown rice, chicken, spinach) only so it could be that. It's still been a long time but I can't flex now without getting cramp, also noticed I get it a lot in the ball of my feet again when I'm in bed, think it's woken me up a few times as well. Looks like something is missing from my diet.
Going to have a google because it'd be interested to know exactly what cramp is, like what are your muscles actually doing when you get it.