I had 2 positive pregnancy test had trans vaginal ultrasound done at 4weeks 3 days from my last LMP and was told no gestational sac seen but that I had a left corpus luteal cyst so could it be an ectopic as I have no bleeding only mild to absent cramps on the left which occur very rarely.

Implantation bleeding has not been scientifically proven even with uterine pregnancies. There are various reasons for bleeding which many people mistake and call it "implantation bleeding."

Look at it this way... something as small as a pencil dot implanting into your uterus causing enough bleeding to be noticed? Nahhh.

How long ago was that ultrasound done? If it was an ectopic pregnancy, by now you would have had to have had it removed or the tube would have ruptured. Ectopics rarely go to the 4th week.

Thanks I had the scan done about a week ago

The IF you were pregnant, it is most likely in your uterus by now.