I have had an ectopic and didn't experience pain near my shoulder blades. The pain was lower abdominal and localised to one side, quite sharp. In my case the pain got progressively and slowly worse over a number of weeks, then rapidly worsened over several hours to a point where I couldn't stand - which was when I was hospitalised (I hadn't known I was pregnant, but I was 8 weeks pregnant at this point). I had also bled when my period would have been due, although this sometimes happens in normal pregnancies too.

How far along are you? For how long have you been experiencing pain? Cramping in pregnancy is quite common, and is often not a cause for worry. If it is ectopic the cramps are more likely to be localised and quite severe, and they will not go away. But if you are at all concerned or think that the cramps are not normal it is best to get it checked out ASAP (even if just to put your mind at ease!).

I hope that all goes well for you and your bub.

ETA: just read your post - if it's been going on for 3-4 days I would get it checked out. If you explain to your doctor that you think it is an ectopic they should see you straight away, unless you have a hospital close by in which case you should go to emergency. Good luck.
I am about 4 weeks and 4 days.

The cramps seem to be all over my abdomen not just one side and feels pretty much the same as mild period pain.