Despite your last period coming on May 21, your due date (which is based on your baby's measurements as seen in the ultrasounds) says you conceived on June 20 or thereabouts. This is not too puzzling since you have irregular cycles -- it just means you had a long menstrual month in May/June. And it does rule out sex on June 1 as producing the pregnancy. I assume you had sex with someone else around the 15th - 20th? That would be the dad.
One other point -- if you are not married to the baby's daddy, arrange for the three of you (daddy, mommy and baby) to get swabbed for a DNA test at the hospital when the baby is born. This is not because the daddy's identity is in doubt, but for the baby's record -- you want to protect the baby's rights to their father. If you and the dad are married, you don't need to do this step because the law assumes a woman's husband is the father of her child born during the marriage. But if not, and later you want to show he is legally the baby's dad, you'll need to have a DNA test, and sometimes it isn't that easy later. Doing the test right at the outset is not only the simplest thing, but it also might be a relief to the guy, and maybe even ease your own mind just a little (though your ultrasounds are obvious). Then you can just go on with your lives.
We are Married..it was one stupid mistake...however i have no doubt in my mind now that my husband is the father...thank you.
I had actually gone for an earlier ultrasound after my 100th test... on the 8th July and only thick endometrial lining was shown. If i did concieve on the 1st...it would have shown a 6 week pregnancy!
Sweetheart, you are in good shape. Never make the same mistake again, and make your husband the happiest daddy in the world forever, that's how you atone. Take care and enjoy your precious baby.