It could be a resporitory (sp?) infection so i would get it checked out by a vet asap to get the correct treatment, they can go downhill quickly. Hope it will be ok. Are you unsure of the sex of charlie? if you post a pic we can confirm this for you.
It's a male
Guinea pigs sneezing is fairly normal as long as it isn't very frequent/continuous. However, if there is discharge from the nose, this would suggest a URI (Upper-respiratory tract infection) kind of like a chest infection. They are almost always bacterial (piggies don't usually get viral infections) and can be cleared up with an anti-biotic but you will need to see your vet right away. If untreated, URIs can deteriorate very quickly and can often be fatal.
Fingers crossed and I hope this helps
x