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The signs you describe most certainly go along with those we see caused by a urinary tract infection. The straining without passing any urine is usually because there is a sense of urgency to pass even any small drops of urine that are in the inflammed bladder, so they never really build up a large amount. That also explains the increased frequency. These signs however could also occur if there were stones that were trying to pass and obstructing her urethra. Fortunately, female dogs are less likely to obstruct due to their anatomy. The vomiting is likely due to the abdominal discomfort and straining.
I would definitely get her in today for an exam and treatment. Your vet will determine after examining her and running a urinalysis, if there is anything else that could be occurring or if any other testing should be done. They will be able to prescribe an appropriate antibiotic and maybe even a change in diet. Once treatment is begun, she should feel much better quickly.
Good luck with her and please let me know if you have any further questions.