I've noticed since spring (after the pollen count has increased) when I open the windows after a few minutes my guinea pig makes a wheezing noise. But a few minutes after closing the window and running an air purifier he if fine... I'm guessing this is a sign he's allergic to pollen, right? This also happens sometimes when he gets hay dust up his nose (I clean it out using a q-tip) and after cleaning out his nose he's fine in a few minutes. From what I've read online usually sick guinea pigs eat/drink/move less, but so far he's been pretty active, wheeking and being a little poop machine. 
I'm always overthinking that he is sick or has a cold... I guess I'll just not open my windows any more
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Just in case, I'll make sure to give him some more vitamin C, and make sure to shake out all the dust from the hay and run my air purifier longer.

I'm always overthinking that he is sick or has a cold... I guess I'll just not open my windows any more

Just in case, I'll make sure to give him some more vitamin C, and make sure to shake out all the dust from the hay and run my air purifier longer.