Hello, and I hope I can help you today. Noticing an ammonia smell after sex is actually a common presenting symptom for type of a vaginal infection known as bacterial vaginosis. Bacterial vaginosis is not a sexually transmitted infection, it is caused by an imbalance of the pH in the vagina leading to the growth of bacteria that can sometimes produce a thin gray discharge and an odor. Any inflammation in the vagina can cause some occasional cramping, so your groin pain is also not an unusual symptom. In order to accurately diagnose the infection, I recommend that you see a gynecologist for an examination. An antibiotic jelly is required for treatment, and a physician will be able to give you the correct prescription. Again, this type of infection is not sexually transmitted, and is as common as a yeast infection. I hope that I was able to adequately answer your question today, and that my advice was helpful. Best wishes, Dr. Brown