Hi Cath
Myometrium and endometrium- different tissue layers in uterus.
"underlying haematoma" kind of like a bruise. Where blood has leaked into the tissue for whar ever reason.
"Retained products of conception" I would presume this means that there is some placenta or the likes still in your uterus.

So it doesn't suggest an infection, but it may suggest there are still bits in there that perhaps shouldn't be. If it is retained placenta you might need it removed, (D&C). if it is a haematoma i would think, depending on the size and location that it would resolve on its own. But i am no doctor!