My due date was nov 13th meaning I conceived on feb 14th to the 20th. Is there any ay jan 20th could be the day I conceived?

It is currently not possible to calculate the date of conception with any degree of certainty, it is all "best guess".

If you have concerns about the parentage of the child then these can only be resolved with a DNA test AFTER the birth.

All predictions forward or backward are approximate. Just because the birth date was Nov 13 doesn't fix the conception date, nor does ultrasound. Jan 20 is not out of the realm of possibility. If you are concerned about who the father is, only a DNA test will be sure.

It is merely a estimate based on size of child.

Since this is a 4 week difference, one way to ask, did you have your period between the 20th of Jan and the 20th of Feb

But while 4 week off is a little out there, it is in the area of possible. So if there were two different people you had sex with during that month period, you will have to get a DNA test to be sure

To Fr_Chuck my periods have always been irregular but my last period started on Jan 15th and lasted until the 20th. I have not had a period since then.

Then it truly could be either. Sorry you will just have to get a DNA test if there is a issue to paternity.