I have a couple of comments, and due to the strange sub-conversation, I only read the posts from Christy. Forgive me if I'm repeating information.
Eating too much hay: A guinea pigs digestive track is designed to keep moving. The fiber in the hay wears down their constantly growing teeth and maintains proper GI function. This means they constantly eat hay and make poop. As long as they get enough vitamin C in addition, this is just fine. Also, if they like hay more than their pellets and you worry about vitamin C, you can give a supplement. Many people here like to use tablets broken into 1/4 pieces. I use liquid and a syringe. Just make sure whatever you choose is sugar free and the only vitamin or mineral listed is "asorbic acid".
Carrots: Daily carrots can damage a pigs liver because it has "soluable Vitamin A". From the other explanations on this board, I gahter that its sort of like smoking. Not everyone who smokes will get lung cancer, and not every pig which eats carrots every day will get liver damage. I figure, don't smoke or over feed carrots, just in case.
Pellets: Don't know if this was mentioned, but high quality, timothy hay based, pellets are what should be offered to your pig. No nuts, seeds, treats, or colored bits.
Scales: I use a kitchen scale from Walmart. It is the 5 lb variety.
URI's come from bacterial infection. Bacteria is always present. When the pig goes through one of the stressful events already mentioned, then its immune system might be less effective, allowing the bacteria to take hold.
Symptoms of mites are soreness, scratching, hair loss, scabs, and a few others. Many people treat all new pigs for mites, because they can be easy to miss and are very painful. If you decide to treat, it is a good idea to treat all of the pigs in your house at the same time.
Good luck, and please post anymore questions.