Sorry, but you haven't given enough information to tell the relationship of the 26th to the situation. You said above that your last day of your last period was the 12th. When was the *first* day of your last period? (I.e., was that the 7th? or the 8th?) And what does the 26th have to do with it exactly, was that when you got together the first time with your present boyfriend so no sex before the 26th would be from the right guy? When was the last time you had sex with the guy you don't want to be the dad? (I.e., if the old guy was on the 25th and the new guy was on the 26th, all the discussion isn't going to help. Too close to tell.)
Ok so does tht mean I would have to have had sex 2 weeks prior to the 26th?
You should get an ultrasound. They can give you an estimated due date with some accuracy (give or take a couple of days) at this point. You can then plug that into a conception calculator and it will compute your most likely conception date.
Doctors start the count for pregnancy on the first day of your last period, and will give you a "gestational age" based on that. (Don't be fooled by the term "gestational age," it does not mean age of embryo based on conception. It tells the length of the pregnancy beginning the first day of the woman's last period. A woman whose doctor says she is "10 weeks pregnant," for example, is about 8 weeks after conception.) So if your period began, for example, on February 7, you'd be considered to be about 9 weeks 5 days pregnant now, but only about 7 weeks 5 days from an assumed conception date.
The ultrasound will look at the actual embryo, measure it and check other indicators, and the doc or ultrasonographer will give you an estimated due date. From that it is an easy computation online to an estimated conception date.
i have also a problem just like yours but mine was much worst.
when was the first day of your last period? by this you can know your due date.