Third eyelids visible? First time my cat has ever been sick :(

About a week ago, I noticed that my cat’s third eyelids suddenly became visible in both eyes. They are white (thankfully not pink/red), and it was very noticeable, which is what prompted me to take her to the vet the next day.

Extra info that might be helpful: there were no changes in food, litter, environment, etc. She is 3 years old, spayed, medium-long hair (I think).

At the vet they did a physical exam and said her eyes themselves looked normal. They explained that cats often show their third eyelids when they’re sick or uncomfortable elsewhere in the body. At the time, her only other symptoms were one episode of diarrhea and sneezing/sniffling that I noticed once. She had a very tiny eye booger during the exam (she does get these occasionally and I clean them), but the vet called it discharge. They said diagnostics could get expensive and would basically be trial-and-error, so we didn’t run any tests. They sent me home with eye drops and told me to use them every 8 hours and come back if she wasn’t better in 2 weeks.

Fast forward to now (about a week later):

-Her third eyelids are still visible with no real improvement.

-She has been sneezing/sniffling more.

-No more obvious diarrhea, but her litter box smells worse than normal.

-I tried feeding plain chicken and rice for a few days to see if it helped, but litter still stinks.

-I’ve also noticed she seems to be grooming her bottom area more than normal (or maybe Im just being over observant i genuinely don’t know about this one..)

-She’s still eating and acting normal otherwise.

I’m worried she may be uncomfortable, even if she’s not in obvious distress. From my own research, I’ve seen possibilities like an upper respiratory infection, GI issues (Haws Syndrome?), or a UTI because of the litter box smell.

My questions:

-Does this sound like something that can be monitored for another week?

-Would worsening sneezing + persistent third eyelids warrant a recheck sooner?

-Does this sound more consistent with a URI, GI issue, or something else?

-Is there anything specific I should be asking my vet to look into without jumping straight into expensive diagnostics?

I’m not trying to avoid the vet if she needs to go back I will absolutely be rushing her there. I just want to make sure I’m doing the right thing and not letting her stay uncomfortable longer than necessary.