It could be either person. Sperm from the guy on August 3 could certainly have been alive in your reproductive tract on August 5. And your egg after ovulation is viable 24-36 hours, stretching things late enough for sperm from the guy on August 6 to make you pregnant.
I am sorry, but only a DNA test will be able to tell. You can get one before the baby is born with just a blood test (you and the guy(s)) but it is really expensive, most people can't afford that kind of pre-natal test. You can readily get one after the baby is born, there are over-the-counter tests and also tests at a lab certified by the court for determining paternity, and the cost is not very high at all.
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