If i had sex 01/15 with a guy a. then i got a heavy period a week later (i heard implantation bleeding can be heavy). i then had sex with guy b 02/5 unprotected no bleeding. an iam now pregnant. who is likely to be the father ?

The 2/5 exposure would be the more likely trigger to pregnancy with the cited story. A NIPS test on maternal blood can detect fetal DNA and verify the paternity. This can be done as early as 8-9 weeks.

After 9 weeks of pregnancy, your blood can be tested for fetal DNA and with the cooperation of the involved men, paternity an be determined. Ask your doctor to arrange the test. For information: https://americanpregnancy.org/paternity-tests/non-invasive-prenatal-paternity-test/