How do I calculate a due date after having a miscarriage???

I had a miscarriage on October 24th and went to the doctor on November 8th and everything was normal. No baby and every test came back negative. I found out on Thanksgiving Day that we were pregnant. Early on in the week I was craving applesauce and chips, and then pickles and ice cream. I told my husband when he was at work to pick me some up. He also got a test that day and at first I saw a faint line with the test and my husband didn't see anything. So my husband said take the test again but I didn't have to go. So I waited till morning and took the test again and it was positive. Now we are trying to figure out the due date. Can anyone help. I'm making a doctor's appointment on Monday.