Physical sickness in guinea pigs

Question
I have two male guinea pigs, Rocky and Ringo.
Last night, I began to clean their hutch and so took them both out for my boyfriend to look after while I cleaned it. He was playing with them and feeding them when Ringo made an unusual noise, and began to vomit a green watery liquid. I separated them as Rocky showed no signs of illness and wanted to make sure he didn't catch anything.
The sickness carried on for around 30 mins, then his stomach seemed to make rumble noises for a while after. He seemed alert.
I have kept him separate from Rocky for the night, and I didn't feed him in the worry that it may upset his stomach.
This morning he seemed OK, but a few hours later, I checked on him again and he has two sore patches on his back. He squeaked loudly when I tried to look at them. I don't know if this is related to the sickness but I have heard little on guinea pigs being physically sick, and have found it hard to find out any information!

I have made a vet appointment but would like another opinion.

Thanks, Becky.

Answer
The sore patches sound like mites, which are microscopic and under the skin, it can cause seizures and eventualy dead if not treated. Guinea pigs do not naturally throw up, are you sure it was not diarrea or coughed up from the lungs? Your guinea pig is very sick, I used to give mine children's kaopectate for diarrea, upset stomach, and everything else in that area. Mites can lower the immune system, causing other illnesses too.
Brittany