may be able to weigh in, but I'm skeptical whether the coronavirus will be accepted as a reason to sit your A-levels over three years, since you would be doing the same subjects. Additionally, all applicants would be affected by it and presumably most will have still done their A-levels in two years.
It's unclear to me why you need to change schools, and you say that you have missed 5 months of learning but lockdown only started on March 23rd. Also schools should have provided work for you to do in lockdown, so you should have been independently working in that in this time anyway.