What Causes Yellow Diarrhea While On Metformin For PCOS?

I m taking Metformin for high insulin levels (I believe mine were at 52 before starting the medication) due to PCOS, but when taking the metformin I get pretty bad diarrhea that is a bright yellow in color. When on the medication it is usually a long while before my bowels turn solid again. (I stopped the medication for about a week & started taking it again regularly and had the same side affects occur both times). Is the yellow diarrhea something to be concerned about?