Skipped periods/pregnant/not sure how far along

I found out I was pregnant on Wednesday. I went to the clinic yesterday and got a positive as well. I skip periods. I haven’t had one since February 7th (I THINK) but I just got my FIRST positive on Wednesday. The clinic had to write I’m over 8 weeks based on my LMP but I know for a fact I’m not . Has anyone ever skipped periods, found out they were pregnant and not very far along maybe 3 or 4 weeks and had a healthy pregnancy ? I’m so nervous because I have no idea how far along I am . I have a ultrasound May 10th. Also is cramping and headaches normal ? I’ve experienced 2 pregnancies resulting in my son and daughter and a miscarriage in-between the two so I’m so nervous/ scared . I