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Yes, possibility of kidney stones with urinary infection is high. Strong ammonia smell is due to protein breakdown. So cut down on proteins. Give a urine sample for testing. Consult an urologist with ultrasound scan.
Meanwhile also consult a gynecologist regarding the spotting. The various causes for vaginal bleeding/spotting after sex are injury and friction, STDs like Chlamydia, gonorrhea, and trichomoniasis, cervical polyps, yeast infections, non specific vaginitis, endometriosis, cervical dysplasia which is a precancerous condition, uterine polyps, uterine fibroids and cervicitis. None of them are conditions that should be ignored. Take care!
Sure could be kidney stones. The foul smelling urine doesn't fit, unless there's a coincident urinary tract infection along with kidney stones, which may be seen in struvite kidney stones. Ultrasound is the safest investigation to figure this out, as there's no radiation involved. If your pain still hasn't gotten any better even after a few weeks I would see your doctor to make the ultrasound urgent, as symptomatic kidney stones left too long can cause problems for your kidneys.