My 75 lb. lab all of a sudden needs to go out about every two hours. I paid attention more yesterday, and it was about that time. Usually she would wait 10 - 12 hours. This has happened for 3 days. She even has awakened me at night. I thought it was peculiar, but it didn't sink in really until this morning when she awakened me again at 4 am. I would assume she has a urinary tract/bladder infection. She is drinking water and eating. But last night she vomited on the floor after eating. Later, I found she had urinated on the rug. She doesn't appear to be straining, and seems to have a good flow of urine. Although she stays outside longer and just stands in one place... as though she might have to go again and she is contemplating it. Otherwise, she appears normal, barking at squirrels etc.

She has never been sick and is almost 8 yrs old. Since it is Sunday, is there anything I can do for her today? My vet isn't open on weekends. Could I give her a couple human antibiotic pills? Will her immune system kick in and fix it without medication?

This info is from a website called PreciousPets.org and contains some really good information. You have said your pet shows only one of these signs of UTI. Dogs can develop diabetes in later years and one symptom is excessive urination same as in humans. Don't give any pills, but see a vet asap.
Urinary Tract Infections

Urinary tract infections are just as uncomfortable for pets as they are for people, and they get them nearly as often. Caused by bacteria in the bladder or urethra (the tube through which urine flows), urinary tract infections can make it very painful to urinate. And, if the infections aren't caught early, they can spread upward to the kidneys, causing serious problems.

Both holistic and mainstream veterinarians treat urinary tract infections with antibiotics, but holistic vets go a little further. They use a variety of natural remedies to strength the immune system so that it is better able to resist the infection. In addition, they feel that it is important to correct imbalances in the body that allow bacteria to thrive.

What are the Signs of a Urinary Tract Infection

There is blood in your pet's urine.

Your pet cries or strains when urinating.

The urine has a bad smell.

Your pet wants to go out more often or is having accidents in the house.
How can you Help?

Safely and effectively treat the causes and the symptoms of urinary tract and bladder infections in pets naturally with UTI-Free, a selected combination of herbal and homeopathic ingredients. UTI-Free keeps pets UTI free without antibiotics. This is definitely one remedy you want to keep on hand at all times, just in case...

Reduce irritation with herbs - An herbal tincture called Goldenrod Horsetail Compound, which contains corn silk, goldenrod, horsetail, pipsissewa leaf, and juniper berry, can help sooth and support an irritated urinary system. Dogs weighing under 15 pounds can have half a dropperful of the tincture twice a day until they are feeling better. Larger dogs can take between one and two droppersful a day. The easiest way to give the tincture is to mix it in your pet's food. An alternative, if you cannot find this compound, is a homeopathic Antibiotic Tincture, which is something every household should have anyway, to help heal a variety of ailments that might normally require an antibiotic.