How to tell if a cat has a cold, and when to bring him to the vet

Hi all, 

My cat, Milo, has heart worms, which has resulted in breathing difficulties that are being managed by my vet. (This isn't what my question is about, but important background.) He's on prednisolone to help him breathe better, and it has significantly reduced his wheezing, but I noticed that his breathing was still very raspy. This raspiness has increased so today (Wednesday) I called my vet. We made an appointment for me to bring Milo in on Monday for my vet to check him out and possibly give him an X-ray to see if there is fluid in his lungs. 

I came home from work today, and Milo had a sneezing attack. His one eye is very watery and when he looks at me, it's usually closed. (He CAN open that eye, but he's been mostly keeping it closed.) It seems like it's a little redder than the other eye, but it's hard to tell. And again, his breathing is still a little heavier and raspier than normal. 

Now I'm just worried that this is unrelated to his heart worms and he just has a cold! My question is: Is it safe to wait until Monday (four more days) to bring him in? 

I wouldn't wait since if it is a URI or eye infection, Milo needs to be treated to prevent it getting worse. Also if you wait, you might have to take him in over the weekend and pay the exorbitant rates ER vets charge.