Thanks everyone. I can't say I'm any the wiser. If you recall, I am now on day 11 after a bleed of some kind. However, on day 3 I had a blood test which showed a peak of luteinising hormone, followed by consistently raised temperatures and tacky cm. All of which suggests that I have ovulated. I explained this situation to the sonographer, who said we'd be able to tell the difference between a follicle and a corpus luteum as the follicle will be round and the corpus luteum more crumpled.
There were no polyps or fibroids, the lining was thin (3.2) and there were some small follicles, all of which were about 5mm, and then an object in the left ovary which was irregularly shaped and 11mm. She seemed to think all in all the scan was consistent with me being in my early cycle and the 11mm thing is the dominant follicle.
I however, disagree. On day 11 I think I would have a thicker lining by now, and a bigger follicle possibly too.
Also, after telling me the follicles would be round, this thing wasn't, but she said my endometriosis might be making it more difficult to see. But my endo was all right-sided and has now been removed anyway. So I think this could indeed be a corpus luteum.
She said come back when I am midcycle (er, I am nearly mid-cycle) to see what has changed and what has happened to this object.
She listed it as a follicle on my printout.
I don't think I can afford another can so I'll just see what happends this cycle and hope my NHS one comes soon.