Unsure due date or weeks along..

My ultrasound tells me I'm 12+6 and gives me a Due date of 3 Feb. My doc says I'm 12+1 and Due date of 8 Feb based of my LMP. My last LMP is May 4 but my husband was gone from April 10 and May 16 (over a month). We had intercourse the day he came back and then days afterwards. So I'm really confused which due dates I should follow.