Irregular Periods, Due date determination

Angela

Since October I have been dealing with irregular periods (again) and I just found out on Fathers Day we are expecting (yay!!)! My last period was April 4th, but due to going to the ER I had a pregnancy test (urine) done on May 31st and it was negative so I figure I had to be only like 1-2weeks then which is why it didn’t show up for them.

So how will my doc figure out my due date since going off my last period wouldn’t be accurate?