Who is father ?

i had unprotected sex jan. 1 09.with an old friend it was a mistake. i had a period from jan 12 to the 17th or 18th of january. on the 17 n from then till now i had sex with my bf. i was still kinda on my period. i found out i was pregant in february. my ultrasound on june 3rd. says i was 20 weeks n 2 days.. somebody please help me whos the father.. i need accurate answers.