Plan B One-Step - Plan B effectiveness?

It's very difficult for anyone to answer your question, because to know that it worked for them, they would have to undoubtedly know that had they not taken Plan B, they would have become pregnant, & that's impossible to know for sure. One person could tell you they were in the same circumstances as you & didn't become pregnant, but will never know if it was because they would have conceived had they not taken the Drug.
You say you were ovulating, but how do you know? If you are going from an app or similar, then that is just a rough estimate, based on the idea that most women ovulate around Day 14 of their cycle. However, not every woman does.
In order to know when you're ovulating, you need to track your temp., cervical position & cervical opening, along with vaginal mucus, every day. Once you've done that for a few months, you can learn to know whether you're ovulating.
Plan B's statistics are based on it being able to delay your ovulation. It is thought it 'may' work in other ways, but these are not claimed by the Manufacturer, as of yet.
If it can do that, then if taken within 12 hours of the unprotected sex, it is said to be 90% effective.
You should not feel burning after ejaculation. You need to get checked out by a doctor, as that is not a common thing to happen. Sperm does not usually cause burning, so something else must be the cause.