How many weeks are you and does your apps says different


I went to my first ultrasound and it says I’m 7weeks and 5days but my doc says I’m 5weeks and 3 days but when I log in my due date it says other wise then I had this app called Flo I’ve been using this for awhile and it shows how many weeks I am and it saying I’m 9weeks and 7days like I’m sooo confused smh like who else going thru this or can somebody help me out I do know I’m 2mntha pregnant but what should I go by tho