Reassurance about cervix/uterus/bladder issues 3 weeks post cs

[Haggisfish]

Hello everyone
I posted this in health as well, but thought more midwives/other CS people might read it here!

I had a successful ELCS 3 and a half weeks ago (my second CS). Consultant doing op noted something in uterus and put ?fibroid on my notes and that was all. On a very early US scan in pg, the sonographer told me there was a small fibroid in uterus. I bled for about two and a half weeks after birth and then it stopped, after I got AB for suspected uterine infection - symptoms were the bleeding wasn't slowing down and was still bright red and I was having lots of pains in uterus. OOH GP said my uterus felt 'bulky and lumpy' and that I needed an US. She gave me metronadizole for suspected uterine infection. midwife said it all felt normal to her and was just going down after CS.

one week later, I have stopped bleeding vaginally, but am getting sharp pain in lower right back, urethra is sore, i'm weeing lots and am getting lots of pain in the uterine area - got AB for cystitis, which seemed to work over the weekend, but symptoms are now getting worse/coming back again.

went back to GP today, who did an internal - my cervix was sore and she thinks there may be a pocket of infected fluid somewhere that isn't being reached by the AB. she took a swab and is arranging an US this week or next. she doens't think it is related to my kidneys or wee, although my wee sample had some blood in it today.

My questions are:
If there was something sinisterly lumpy in my uterus, would it have shown up on my scans in pregnancy and/or during the cs?

Has anyone else had anything like this - I can't think how they would treat a pocket of infected fluid, other than try to syringe it out somehow?!

Could it just be recovery from the CS?

i'm EBF and still feeding my 2.5 yr old - last time I had problems with low oestrogen and vaginal/urethral dryness and irritation because of this. Could it be similar this time?

thank you and sorry for the mammoth post!