Honest to God you are going to push yourself over the edge. I wish you were here, in my sitting room. I shake you, then hug you!
You will not get any clearer an answer than you have now going by dates. You really, really won't. Please try to accept that.
You are pregnant with a lovely little girl.
Your partner is over the Moon.
Your DS is happy.
Do you really want to mess all of that up?
If you keep on obsessing, crying, not eating you are going to end up blurting it out to him, making yourself I'll, upset your DS and really not do your DD any good either.
You made a mistake. Now is not the time to tell your partner about it, if ever.
It is more than likely his, much much more likely.
Put it out of your head. Read my previous post, please.