Hi all, I'm just looking for some advice..

3 years ago I had a colposcopy after irregular bleeding and they didn't find anything at all - the report to my GP said my cervix was entirely normal. I was due a smear at the time but didn't go because I thought the colposcopy would be sufficient.. fast forward 3 years and I've just received my results to say I have high grade severe cell changes. I have a colposcopy appointment on Monday. My confusion is around how the cell changes happened so quickly? Is it really possible to go from an 'entirely normal' cervix to severe changes in just 3 years? I thought cell changes took many many years to happen. Could the last colposcopy have missed something?

Any advice massively appreciated!