Ectopic Pregnancies

When would you most likely know if your pregnancy is ectopic. I worry so
Much! I am 7 weeks and just curious if I can stop worrying that I am all of a sudden going to have some excruciating pain and have to go to the dr. I know everyone is different but around how many weeks would you start feeling pain and bleeding? I won't go for my first ultrasound for 2-3 more weeks :(