Hi and welcome
I am very sorry for your continuing issues. URI can sometimes take longer than just a week's medication to cure.
Can you check by holding your ear to the nose/throat area and then to the chest whether the wheeziness is rather coming from the upper airways or down from the lungs? Can you try to see whether a bowl of steaming water next to the cage is easing the breathing?
Is it just the wheezing that is persisting or the heavy breathing? We strongly recommend to see a vet. How piggy savvy is yours?
We have got a recommended UK vets locator on the top bar.
Are you weighing your guinea pig daily at the same time in the feeding cycle instead of the usual weekly weigh-in to check whether its food intake is steady? Up to 80% of the food intake is hay, which you cannot control. The need to breathe comes before the need to drink and thirdly the need to eat. Loss of appetite and only then loss of thirst are typical for a severe URI or pneumonia. It is not helped by the fact that antibiotics often act as appetite dampeners.
As soon as there is a weight loss over 50g or more, you start topping up with syringe feed and water. If the weight loss is within 24 hours, you need to start feeding round the clock. If a piggy loses 100g from one day to the other, it means that it hasn't eaten or drunk at all in that time and its guts are in danger of closing down. That is an absolute emergency.
Our step-by-step syringe feeding guide also contains tips on what you can do with what you have got at home in an emergency.
Complete Syringe Feeding Guide
How old is your guinea pig? Have you had it for long?
Since we have got members from all over the world, we find it helpful if you please added your country, state/province or UK country to your details, so we can tailor any advice to what is available and doable where you are, including vet access and stand of knowledge, as well as climate, which can play a role with respiratory problems. Click on your username on the top bar, then go to personal details and scroll down to location. Thank you.