Brief Answer:
Not really

Detailed Answer:
Hello,

vaginitis is a benign disease that is cured easily most of the times, so it's not serious despite the symptoms it may cause.
Blood in the urine can be found in some serious diseases and warrants thorough investigation of the urinary system.
Was the blood visible?
Did you have symptoms? What symptoms?
Recent antibiotic use?
History of vaginitis?
Answering the above questions, would help me suggest an investigation strategy.

Kind Regards!

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Brief Answer:
It doesn't sound so serious

Detailed Answer:
Hi,

Vaginitis is a common "side-effect" of antibiotics. Normal flora of the vagina is destroyed and pathogens take up their place, causing vaginitis. Vaginitis may present with burning, itching, pain or discomfort when urinating, vaginal discharge and a bad smelling vagina. Very light bleeding can be justified as well.
This is not a serious condition and it can be cured very fast. You need to visit your gynaecologist who will guide your treatment.
Since blood in the urine can be serious, I would suggest double-checking that it was due to vaginitis by repeating the urinalysis after successful treatment. Having symptoms of vaginitis that followed antibiotic treatment suggests that the blood can be attributed to it with a high grade of confidence (99,9%)!

I hope I've helped!
If you'd like more information, please let me know.

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