Marcie asthma?

So since I got Marcie over 4 months ago she's been a little wheezy when she breathes. So naturally I took her to the vets. They took an X-ray and saw what looked like a little mucus in her lungs so we treated her for a URI. But after treatment she was still wheezy. I didn't have the money at the time to take her back to the vet so I waited and just kept an eye on her. It's been 4 months she hasn't gotten worse, she hasn't gotten better. Some days she's not "clicky" at all. And other days it's worse. She's a very timid rat and so when she gets a little stressed (I pick her up) it gets a little worse (because her breathing gets heavier). My other 2 rats so no sign of any sickness though. And other than that noisy breathing and her timidness Marcie seems completely healthy as well. No poripheren around the eyes or nose.
Any idea what's going on here? I was thinking maybe asthma but I really have no idea....

What antibiotics was she on and for how long?

The X-rays showed mucus or a spot in the lungs? A spot could mean abscess. I would keep her on Baytril for life if that's the case.

She was on Baytril and something else that was yellow... And only for 10 days... Which I know is not long at all... But I didn't get worse so I wasn't too concerned... But I think after I get my next paycheck I will look into going back in and getting another X-ray and seeing what my vet thinks if you all think there is something up. She was only able to get a top view of Marcie cuz she wouldn't lay on her side long enough to get another view