How quickly can cells change?

So I had lletz treatment in December 2014 for CIN 2&3, I was seen for a Check up in May 2015 and advised the margins were clear after treatment, all looked okay and I tested negative for hpv.

After Christmas I started to have excessive discharge again which was a major symptom for me last time so I went to the doctor and he just referred me straight back to the hospital for a colposcopy.

I went last week and The doctor sat telling me how unlikey it was to have abnormal cells again as my treatment was successful and I was clear of the hpv virus. However when she had a look she took 2 biopsies and said there were changes again and I would be returning for treatment but which treatment would depend on the results. ( I should have asked more questions but I was sore and upset it had returned and just wanted to go home)

I guess I’m asking has anyone else had abnormal cells return so quickly after being told you were clear of the virus? I’m starting to wonder if they got it wrong back in May!
And is it normal for changes to come back so quickly?
Tia xx