Last cycle was 4/25 had sex 5/10 took plan b 5/11 had sex again 5/16 now I'm pregnant. Which time Do You think I got pregnant?

Can't say. It is impossible to say for sure without knowing your cycle length when you would have ovulated. Plan B has a 5% failure rate even when taken immediately and conception can occur as the result of sex a few days before or after ovulation. Plan B taken before intercourse is not protective. If there were 2 different partners you could tell with paternity tests. Hope this helps.