Have you had anal sex with your boyfriend? Did the odour appear after you were dating your ex? if so,most probably is because of the anal sex. I believe that when guys do it from the back,it transmits bacteria which harms the bowel of your own body. I also had a boyfriend who I found out later was bisexual,and I got this odor problems after... i am not sure 100% if this is the cause but making some guess and makes sense...