4 month old boxer in heat?

Question
Is it possible for a 4 month old boxer to go in heat?  My pup has been peeing more than usual and today I noticed blood in her pee.  She's also been eating less in the last 3 days also.  I'm taking her to the vet tonight but any insight would be great.

Answer
Possible but unlikely. She most likely has cystitis which is a burning from a bladder infection. The blood is from the bladder being really irritated and raw. She could even have bladder stones.

She is in pain, thus the lack of appetite. Make sure the vet checks her for stones.
Her vulva would be really swollen if she was coming into heat.