AWWW, Girl I know you are worried, and it tares at your heart! Anyway, My HYDRO, my pug mixed was doing this and took him to the vet and he was backward sneezing! Almost like he couldn't breath and was snorting at the same time. I was concerned , vet said it was normal! All my little dogs do it, You just rub their little throats, and comfort them until it passes! Well, I hope this helps and gud luck to you and your little pooch!
Was going to mention possible reverse sneezing too, not uncommon in those breeds.
Your dog is a mix but I suggest you do a Google search on each breed to see what health issues they can have, might help you out.
Often the National Breed club web sites will address health issues also and give you some insight.
If you are treating for Giardia, good thing that was discovered. Often does not show up in every stool. Make sure you wash the bowls daily in hot, soapy water or diluted bleach. Try to confine the dog to going potty in one area and clean right away and you can spray the area with a diluted bleach solution. Wash bedding, etc and keep your hands washed.