Could it still be a bacterial infection even if it goes away and doesn't come back until sex again!! And I know it can't be a new persons semon because it's happened with another person before also and we've had sex several times...And I also can't really go to the doctor because my madre doesn't know I am sexually active...
It could be an allergy, yes, but there are other possibilities as well. If you have only very recently begun having unprotected sex, a new person's semen can cause an immune response, and your body will treat it like a foreign object, bacteria, or virus. The good news is that if this is the case, it will eventually go away.
Do you have allergies to certain chemicals found in soap or chemical perfumes (like the stuff they use to put scents into soap and detergent)? It could potentially be whatever soap or body wash he uses on himself, or even the detergent he uses to wash his underclothes. (Seen that happen, but it took forever to figure it out, so I'm throwing it out there.)
The vagina is an acidic environment normally, the pH is high, whereas semen is highly alkaline in composition - remember from your first year of physical science/chemistry what happens when you mix an acid and a base? It could be that his diet is causing strongly alkaline responses in his semen OR (and this is more likely) you might have a bacterial infection in your vagina causing your pH to increase.
Sometimes you can carry them around for months or years and not know it...there are far more things out there than just the generic yeast infection. Go to your Gyn and have her check for possible issues, and test you for STDs and bacteria.
Hope this helps.
It is true that some women are allergic to semon. Just like some women are allergic to condoms. It could just be your allergic to his particular semon, and not every other mans. Ask your boyfriend if he is eatting anything that you are allergic to.