If you are at all worried about the health of your cavy even if it is just a hunch, please get it to a good vet as soon as possible and seek proper medical attention. The best piece of advice I can give is to find a good cavy vet, with an emergency service before you need one.

Guinea pigs hide illnesses very well. In the wild this means they are less recognisable as the weakest of the bunch which predators will go for first. At home, this simply means that by the time your pig is showing signs of illness, it may well have been unwell for a while and is probably in need of urgent treatment to survive.