Omgness this is so weird haha, i just clicked on the Health and Illness thread to post a new thread on my piggie doing the same thing but then i looked down and saw your thread! last night we had Sugar out running around in the kitchen when she weed and some blood was mixed in with it, we don't know whats wrong...but this has happened one time before with her last year and we googled "blood in guinea pigs urine" and it told me all about it...
Blood in a pigs urine is usually associated with Estrus and is NOT a serious condition unless she is unable to urinate or stops eating. We do not usually give pigs antibiotics because they can cause problems themselves.
You will need to increase her vitamin C because a pig under stress requires 2 - 3 times the normal C ration. In addition, put a little bit of unsweetened cranberry juice in her water daily to lower the acidity of her urine. You also want to encourage as much drinking as possible.This will help to restore the balance in her urinary system.
Give her some cut up cucumber as this is a diuretic. However, discontinue all sugary fruits until this problem resolves.
We did all of this and jer little problem went away in no time =) Cranberry juice and non-sugary fruits will do the trick

We even called the vet and asked if what we were doing would work and they said it should work, so we tried it and WA-LA!
And now it's happening again with my piggie and just started yesterday, so i've gotta do this method again with her to make her awww better
Try this with you're little pig and see how things go

p