The father to my child

I got my period and the last day was January 24th I had sex with 2men after,once with partner 1 and about 4-5times on February 1st-2nd.I was being cautious of being pregnant so I took 2tests daily throughout january because I find out I'm pregnant every February...everyone of them even the digital ones came up negative.I took a test feb.3rd and it was negative and I left for vacation on the 4th and came back on the 11th and it was positive....I'm worried who is the father?? The doctor said I was 9wk on march 25th but she goes back to my menstrual period and it does not make sense or add up for me........
I just really need to know