Having been tormented by this on and off, in desperation I applied Ivermectin to this external delta of Venus (being careful to not allow it onto the inside tissues) at night. The next morning, no more odor. In fact, I had much less sweating. I have done this for 3 nights now and so far the results are stunning. Last night I put some ivermectin under both of my underarms and this morning -- absolutely no odor.
This is the ivermectin I use: "Ivomec For Cattle & Swine Injection" Don't worry, you don't INJECT it for this. Just use very lightly as a topical. Less than a thimbleful goes a long way. Start with half a thimble. I mean literally a thimble, not the little cup that comes with the ivermectin product.
I'd rather find something more "natural", of course. But I think that doing the ivermectin for a while will get me ahead of this problem and then I can see how well vinegar or tea tree oil or grapefruit seed extract and other suggested remedies work.
My thought is that the odor is caused by an overrun of skin parasites. The ivermectin is intended to kill various parasites.