Yes it is a side affect of it just wear a panty liner
Do you mean when on progesterone capsules? Are the suppositories yellow? The progesterone suppository capsules I was prescribed were white and powdery if you opened the capsule, like powdered sugar in appearance. They did give me lots of messy discharge, but it was certainly not yellow -- it was chalky, sticky and white. Maybe there are different types of progesterone suppositories, but the idea of the discharge being yellow and smelling seems very unusual. If that happened to me when I was on progesterone I would assume I had gotten a yeast infection or a UTI.