Dog poop issue, is it a problem?

my 9 month old albino chihuahua has been doing pretty solid poop normally, unlike that last few days in which he was doing a lot of diarrhea. But the only thing I'm left wondering about is if his poop is normal. I took him for a walk and he pooped solid poop, normal brown color, and another... Turd... That was sort of yellow in appearance. The brown colored one had mucus in it. Should I be worried? His poop has been returning to normal from the last few days, as I said, he had diarrhea. Anything I should be concerned about? Is it mild or severe? The yellow turd was solid, like a normal poop, but it was just yellow. Don't forget about the mucus. If he has an infection, how much does the drug/treatment cost?