Sweetheart, if your first ultrasound was at 25 weeks, and you are getting a due date based on that ultrasound, the margin for error is a couple of weeks, I'm afraid. You will need a DNA test once the baby is born, to sort this out. Test both guys.
my due date is december 31st the first time i went to the doctor they told me i was 25 weeks along wich counting back at the time was exactly the first week of april but like you said thats not how it works i still dont understand who it could be the first week of april or the 27th of april?
It is true that you do not count the weeks and then say, aha, at "day 1" of all those weeks ago, I had sex, and that is who the dad is. They begin the count at day 1 of bleeding, of your last period that you had before getting pregnant. Or, of a computed day 1 of bleeding, if the woman does not know for sure when her last period began. They do this because they need a definite start point for the count, not because they think you were pregnant on day 1 of your period. (They know you weren't, you were having a period!) They then compute in an allowance of 14 days to get you to the point where an average woman would have ovulated, and assume you conceived around that time.
When did you get your first assessment of how many weeks along you were, and what did they say at that time? Do you have a due date?