I Had Sex On The 19th And 24th Of July

I had sex on the 19th and 24th of July with 2 different guys. I have irregular periods & my last period was June 7th-12th. I had a positive pregnancy test and went to my first appointment on August 27th, 2015 which measures the baby at 0.65cm & me being 6 weeks 4 days. My expected due date is April 17th, 2016 & that puts my period at July 12th, 2015 says the doctor. Can you help me figure out which partner may be the father and when I conceived.