Hello, this is my first time posting here.  
Could this be a Giardia cyst? The first four pictures are from today (May 28th). I think the fifth and sixth pictures could be a trophozoite (also from today). The last two pictures are from yesterday (May 27th). It is a basic wet mount with physiological solution. Magnification is 1000x.

I have two cats. When we got them from a shelter, we were told there was a possibility they had giardiasis. One had diarrhea, so we had a coprology test done, but they didn't find any Giardia. They still prescribed antiprotozoals, and we changed their food, which stopped his diarrhea. Then his brother started having diarrhea problems (he didn’t have them before). We consulted a vet, who told us it was probably due to the new food. We went with that and started switching to different brands and adding probiotics, but nothing changed. His brother, who initially had diarrhea, is completely fine now and has normal stool. I am currently studying for my finals and a parasitology exam. I have a microscope and *very basic* training, so I was curious if I could find anything, even though there is a low chance of seeing anything in a wet mount. 

Regardless, I am calling a vet today.

Parasite identification (magnification 1000x)