Rosie, I am experiencing lots of cramping and pulling on my left too. From what I understand, your uterus leans right and as it starts to fill with blood and fluids, it pulls on those muscles and can cause quite a bit of stretching.
Did you pee on more than a few sticks? Usually ectopic pregnancies will have low-rising beta levels. Not typically darkening tests and blood serums. That is what my doc told me. Plus, most ectopics also produce some bleeding beforehand. Spotting or light flow. Since the vascular system in the tubes are more sensitive than the uterus.
But I am experiencing a lot more tugging and cramping than I remember with any of the others. Which could be selective memory (I was reading back whe. I was pregnant last time and it seems I did experience some pretty intense sensations in that regard). So maybe it's normal of a fourth pregnancy?