I presume you mean that you have undergone LLETZ.
The collection inside the uterus
may be due to the scarred cervix
that blocks the opening and does not allow the uterine fluid to come out. It is less likely that it has been present before your surgery. If you have any ultrasound
reports performed then, just check them to see if there is any collection.
If you came with similar complaints in my clinic, the first advise would be to drain the fluid and analyze it for any abnormality.
It is unfortunate that the attempt to drain it failed maybe due to the tight cervix.
It is difficult to say what caused the increase in echo and if there is blood in it unless the fluid is drained and examined for blood. Though a trauma during surgery is a possibility.
However, I suggest that you better undergo the procedure under anesthesia
as it is easier and if you do not feel confident, you may concern another gynecologist for the procedure. However such events are rare but they do occur depending upon tissue status. I feel that under anesthesia you will not have any problems, the cervix may be easy to dilate and may not reclose in future and you will know what the fluid is and if you need any further treatment.
I understand your concern, but you will be allright once this gets over.
Hope I was able to help.
Take care and goodbye.