Hi and thanks for the query,
this could be certainly an inflammatory reaction, considering the fact that you are both faithful to each other. However, traumatic conditions could also cause this. Other infectious causes, not actually sexually transmitted conditions could also be responsible for this condition. Clinical evaluation by your general physician shall be recommended to draw the borderline between an infectious and a non infectious cause for a proper management. Consulting your primary care
physician is the recommendation step to take.
Thanks and best regards,