So a few things -
First, you don't get symptoms of an STD that fast (the next day). The absolute minimum is 2 days, usually a bit longer.
That you had symptoms the next day suggests either panic or dehydration, bladder irritation from alcohol/caffeine, etc. It was not from an STD.
Did you receive or give oral sex? You don't mention this, but if you only gave, you can't have a genital STD.
Cysts on the vagina are quite common, there are a few different kinds, and aren't related to STDs.
Perhaps the most telling - when you aren't focused on it, you don't have symptoms. You can go long periods without symptoms. If you had an STD, you would have constant symptoms - they don't come and go.
You've had several different tests, and they are all negative. You have to trust the science at some point. Guilt is making you think irrationally, and there is no evidence you have an STD.
You've been married for 15 years - I'm guessing you are in your mid-30s, at least, as is your wife. It taking time to conceive isn't unusual. Does her GYN know that she is trying to conceive? If she is 35, they may want to do some tests sooner than they might if she is younger.
Please try to let this go. It's not an STD - your tests confirm it.