Hello, my name is***** and I have over 20 years of experience as a veterinarian.
Dogs continue to cycle throughout their entire lives, they do not go through menopause like people. She may have been having silent heats or such small amount of discharge that she was able to keep herself clean and you weren't aware of them.
This cycle sounds like an abnormal heat cycle with heavy bleeding that has continued longer then usual.
Because she seems "bloated" (has seemingly gained weight) isn't eating as usual, and is moving slowly I am more concerned.
An increased vaginal discharge can indicate endometritis, which is due to a thickened, abnormal uterine lining. This wouldn't necessarily be dangerous for her, but it would indicate that she likely has abnormal fertility because of her thickened uterine lining. This should not lead to changes in appetite or weight gain.
Another reason for an increased discharge can be a uterine infection called a pyometra. 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. As the uterus enlarges it can make their abdomen look bigger.
Early on the symptoms of an open pyometra and endometritis can be very similar as long as the pyometra is draining. That is because if the infection is draining she may not feel the effects of the bacterial toxins as quickly as if the infection was closed in and the toxin levels build up more quickly in her uterus and bloodstream.
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 differentiate between endometritis and an early pyometra. Today would be best because her appetite is off. 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.
Please let me know if you have any further questions.