I have been having shots of pregnyl twice weekly so my fertility specialist was almost positive that it was the corpus luteum rupturing that was giving me the grief - apparently the pregnyl really exacerbates the condition. I was also told that 4 weeks was really much too early to be feeling an ectopic (from memory I didn't have pain with my ectopic until I was closer to 8 weeks). I then had a routine scan at 7 weeks which confirmed bubs was where he should be.

If you're still anxious about it maybe you can get an early scan, although at this stage you might need to have an internal one.