How Long Can Sperm Stay Alive After Ejaculation?

Hi, I want to know what the likelihood of pregnancy is if a man had ejaculated and I had gotten some semen on my fingers. Then, wiping it off with tissue paper to the point where hands appeared dry before touching the vaginal opening after approximately 5 minutes. I am scared because I read that many period symptoms are similar to early pregnancy symptoms. As well, I have had light vaginal bleeding following the incident, but I assume it may be from my hymen breaking. However, I also read that spotting can be a sign of pregnancy as well. How long can sperm stay alive after ejaculation? Is it true that sperm needs the seminal fluid from ejaculation to neutralize the pH of vaginal fluids? Thus, a finger that had been dried and wiped of semen would not have been able to carry viable sperm to pregnate, as the pH from the vaginal fluids would have killed the sperm? Thank you