Help! Is my guinea pig sick?

I just got three guinea pigs the other day, and my one baby, Duck, has been showing signs of an illness of some sort. She hardly mostly only moves to go to a hideout or to eat and refuses to join in with the other piggies to play. She often sneezes and is always sleeping which concerns me. She has a large cage,... show more I just got three guinea pigs the other day, and my one baby, Duck, has been showing signs of an illness of some sort. She hardly mostly only moves to go to a hideout or to eat and refuses to join in with the other piggies to play. She often sneezes and is always sleeping which concerns me. She has a large cage, playmates, plenty of water, hay, and vegetables, yet she still doesn’t engage in activity. If anyone knows what could be wrong with her please reply asap.
P.S. She was already bonded with one of the guinea pigs, and the baby monitor we have set up shows she does the same things even with nobody around.
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