What is the first major sign of ectopic pregnancies, how intense is the shoulder pain and what week does the shoulder pain usually start.

Don't use symptoms. If you've had a positive test, most ectopics are pretty silent until about the 5th week at the earliest. Are you at risk for ectopic? If so and you are pregnant see a doctor asap, do not wait for symptoms. By the time you have significant shoulder pain you are already in deep trouble.