I'm sorry you're having such a hard time with this.
I find it strange that your healthcare provider didn't find any imbalance or infection: might you be able to get a second opinion from another provider? Like you, I trust your sense of your own body, and it seems very odd to me you're experiencing a strong, fishy smell without there being even a trace of a bacterial or other infection.
In the meantime, I can make a couple suggestions:
1) Overwashing can actually create imbalances, and you absolutely should not be using soap *inside* the vaginal opening at all. If you're doing the latter, you'll want to stop. That might be part of the problem. same goes with washing so often. I'd try and limit it to once a day, and you might even want to stick to just using warm water for a while, not soap at all. The vagina is actually self clearing, and the vulva does pretty well on its own, too. In the event you aren't willing to try that, how about switching the brand of soap you are using, just to see if that's part of the issue?
2) If your boyfriend has a penis and is ejaculating inside of your body when you have the kind of sex where he can, I'd take a break from that for a while, too, either having him use condoms or just withdrawing.
3) Speaking of condoms, are you using them?
4) How about your undergarments and clothing: are you sticking to looser undergarments (not thongs and such) made of natural fibers (like cotton)? If not, I'd switch.
5) In the event that you've got a sensitive nose, so you're smelling something, but it might not be as strong as it is to you, and so might just signal being on the edge of an imbalance, you might try taking a probiotic supplement. The good ones can be found in natural foods places (or stores with a good natural foods section) in the cooler. A round of probiotics can often move a very mild or slight imbalance back to the good place.
6) On a similar note, how have you been eating? If you've been eating a lot of junk food, meat or dairy, that can make body odors, including with your genitals, smell stronger. If that's the case, see what you can do to make some healthier changes. Drinking more water can help, too (if your urine smells stronger, too, this can be an indication you're not hydrated enough).
If none of that changes anything -- and another provider doesn't find any infection or imbalance, either -- then one other option, given your age, might be that you are just having some hormonal changes that are causing your vagina/vulva to smell stronger than it used to. That can happen during puberty (which lasts into your twenties), and for someone with a very sensitive sense of smell, it might smell extreme, even though it really isn't.
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