From your two ultrasounds, I get November 16 or 17. Not the week of the 30th. Not the 26th.
Plan B does not always work, because it has to hit at exactly the time the embryo is attempting to implant. Even its literature says there is a one in eight chance of it failing.
The sperm from the sex on the 14th and the 15th would have been alive for several days after the sex.
I am sorry you're mad and think he's lying, but it really does not sound (from your ultrasounds) like the baby came from any of the later times.
You probably get a lot of folic acid in your diet, you can google dietary sources of folic acid if you would like to put those worries to rest. You can certainly begin to take prenatals now, even though the folic acid is beneficial before pregnancy you will definitely need the iron throughout and more later than earlier.