Man B is the only probability, especially as you had a period after having sex with Man A. Not to mention how low your HCG levels were. Not to mention that you got a positive OPK and had sex when you had a positive OPK. And not to mention that you didn't get a positive until about 2 weeks after estimated ovulation time.
It's Man B.
I agree with what Scrib7 said with your HCG level that low you are early in the pregnancy so i would also say that man B is the daddy...Good luck to you and happy 9 healthy months.......
In my opinion with low HCG levels you are very early pregnant so I would say man B. If you had a HCG blood test done then they should tell you how far along you are that would help you figure it out. Good Luck.
I think b also but if you ovulated early a could be the daddy so I would on the safe side let them both know you are pg and take things from there. It doesn't matter if a came inside there is still pre stuff and it only takes one. Best wishes to you. Good luck.
AP
If I had to guess (which is all this is!), I would also say it sounds like Man B is the father.
But Like Ziggysgrl0724 asked, I am also curious - were you trying to get pregnant from Man B?
it sounds like man B is the father, but I am no expert. Can I ask Why you were using OPK's? Were you trying to get pregnant? If so which man were you trying to conceive with?