I Had A Period August 5th , I Have 34

I had a period August 5th , I have 34 day cycles . I am now 12w6d as of November 9, 2015 . I had sex August 18th with someone and then had sex with someone else on 20-25 . I am not sure if the guy on the 18th ejaculated in me , I don't think so but pre cum can cause pregnancy , but the guy on the 20-25 did indeed ejaculate in me . Is there any chance the guy on the 18th is the father ??