What Causes Strong Odour From Vagina?

My boyfriend of almost 7 months has twice in one week had a vagina smell and taste on his penis after showering! Our sex life and his cleaning habits r the same,,although he does have alittle heat rash in the crease of his leg next to is ball sach witch is new, he says thats the reason for the vagina taste and smell. Its very strong odor. Is that rash the reason for the taste and smell? Nothing has changed with my vagina the odor of vagina smells nothing like mine. What could be the cause and how do we take care of that little rash because I have lots of orAl sex with him and cant bare it with this issue please help me . Thank you angela