Fluid in uterus?

I had my baseline US today and I’m very frustrated. I was told that I have “fluid” possibly blood in my uterus. I finished BCP last Tuesday and had a very light period on Thursday-Friday and it went away. She said we wouldn’t be able to do a fresh transfer after the retrieval if I have this fluid. She said it may go away on its own though. I’m also on Lupron. We’re doing the long protocol.

Does anyone have experience with this? I know it’s not the worst news but I just want to stop prolonging things. We’re starting GonalF on Saturday and my next US is next Wednesday.