I was probably baptized when I was a child, however, since there aren’t witnesses, I will be baptized conditionally, confirmed, and receive First Communion. I will be confessing my sins on that same day before conditinal baptism. Will the confession be valid?
Yes. If there is reason to believe that you may have been previously baptized – as indeed there is such reason, given that you will be baptized conditionally – not only can you go to confession before conditional baptism, you should. The only time you would not go to confession first was if it was known with certainty that you had never been baptized. In the case of someone who had never been baptized, baptism washes away original sin and all personal sin committed up to that point.