Don't remember reading any direct correleation between sulphur and dark circles. I guess there could be.
Minoxidil can cause this if you're not washing your hands properly - as with any other dilator. Lack of rest, blood circulation, Vitamin K deficiency , too much sun, maybe iron deficiency , hereditary, allergies or excess rubbing of the eyes, and a host of other things could cause dark circles.
I would check your diet. Since you stopped taking minoxidil, I guess it's not that.