I had sex with my ex on the last day of my period which was on January 24th, no condom as for he pulled out before coming. I had sex 3 days later on January 27th with my boyfriend, as for him also no condom and he did finished inside me, According to my calendar my ovulation days were from Jan 30-Feb 5. So now according to the clinic (not the ultrasound) I am 6 weeks pregnant. At this point I don't know what to do, who exactly could be the father of my unborn child?

I had sex with my boyfriend on  January 4th (no condom finished inside) January 13 (with condom) January 27 (no condom finished inside)  & February 11 (no condom finished inside) 
With my ex only on January 24 (no condom but pulled out)
Based solemnly on that who might be the father?

Who 'might' be the father? Either one, of course. There is NO test that is accurate other than DNA after the baby is born. Not ultrasound, no estimated ovulation days, not what the doctor estimates as conception date, nothing.

Thanks for your straight & honest response.