NUMBER ONE RULE of vaginas - don't ever use perfume around them. Ever. That includes scented soaps. It's frustrating to have to deal with one when you shouldn't have one, but the fact is that the vast majority of vaginas out there are super sensitive and their owners don't even know it. Throw out the perfumed 'lady soap' and buy something organic, non-perfumed, preferably soap-free. The detergent agent in soap-free products is usually coconut so if you're allergic to that avoid it. Soap-free is best for between the legs because it's non-drying and therefore non-irritating. It won't strip the oils out of your skin like regular soap.
Next, buy two over the counter yeast treatment kits and use them back to back. Name brand is best but a pharmacist may be able to tell if a generic has good results.
If that doesn't work get checked for an STD. Years ago I got trichinosis from an ex and I had a very fishy smell that wouldn't go away. I got tested, took the medication to treat it, and tada. Smell went away. It's very easy to get an STD and they can lurk for years. The affects of them can come and go. Most of them are treatable and county health clinics will often do testing/treatment for free or dirt cheap.