Hello and welcome to the forum! Did you buy your guinea pig from a pet store?
The milky liquid you are talking about might be the calcium deposits guinea pigs make when too much calcium is in their diet. Try easing off of high-calcium foods for a little while and see if the milky liquid goes away. You want to avoid parsley, dandelion greens, collard greens, kale, mustard greens, and turnip greens. Stick with some type of lettuce (butterhead, romaine, red leaf, green leaf, endive, escarole are all good choices) and a slice of bell pepper each day as staples and try a few other vegetables each day as well. You want to focus on variety, providing about a cup daily of a mix of vegetables. Check out the
vegetable charts for more assistance.
Have you considered getting a friend for your guinea pig? As social animals, it is really quite an essential that you adopt a friend for your guinea pig. If you got your guinea pig from a pet store, you will want to
sex her first to double check that she is a girl. If she is indeed a girl, you should go look for another girl or a neutered male guinea pig at your local shelter or on Craigslist.
Petfinder is very helpful when looking for a guinea pig for adoption, as well. Read
this before adopting a friend for your guinea pig, making sure to quarantine the new pig in a separate room for three weeks and introducing the two pigs on neutral territory. Some rescues or shelters even assist with introductions of the two pigs, so ask about this service.
Good luck! This forum is a huge wealth of information, please stick around!