Hello, my name is***** and I have over 20 years of experience as a veterinarian.
I am sorry to hear that your pup Summer is behaving in an unusual manner, not eating well, drinking lots of water and has red eyes.
Pregnancy is not likely to create these symptoms.
If she had a recent heat cycle then I am more concerned that she may have a uterine infection called a pyometra.
Dogs with an open pyometra (open cervix) usually have an increased vaginal discharge even when the normal heat ends. Dogs with a closed pyometra have a closed cervix, so the discharge cannot drain and it builds up inside making them feel sicker.
These pups drink a tremendous amount, eat poorly and are lethargic due to toxins from the infection.
Pyometras can rupture, causing peritonitis and/or the infection can spread to her other organs leading to abscesses in her kidneys, liver spleen and even her heart valves. The toxic metabolites from the infection can affect her appetite and cause her to drink lots of water as the infection progresses.
Antibiotics alone do not work to treat a pyometra as they have poor penetration into an infection filled uterus and do not address the pool of infectious material and toxins in her uterus. We sometimes use prostaglandin injections and combination antibiotics in dogs that owners want to breed another time, but the success rate is variable. And even if it works if she isn't bred successfully on the next heat the chances of the infection returning are very high. At her age it is unlikely that she would be a good candidate for breeding anyway.
Ideally she would see her veterinarian for an examination and to check her vaginal discharge to try and determine if this is indeed an early pyometra. The sooner that she is examined the better as if this is a pyometra the sooner that is addressed the better chance she has of doing well. Treatment for a pyometra is stabilizing her with intravenous fluids and antibiotics and surgery to remove the infected uterus. The longer that you wait the more opportunity this infection has to spread and the more difficult it will be to save her.
Since her appetite is off and she seems to be drinking more water then usual, especially if she is running a fever (rectal temperature greater then 103F) then this probably should not wait, she should be seen as soon as possible.
Other reasons for her symptoms include other systemic infections, organ failure or diabetes. Those are also all serious conditions that require quick veterinary intervention.
Please let me know if you have any further questions.