School Phobia

Hello, Sorry it's my first question so I would really appreciate any advice given. When I was in year 11 (Year 12 now) I developed separation anxiety and School phobia. The school phobia has been a real big issue in my every day life since then. I was allowed to be home schooled for a year because the school was able to finance it but since im older now, home schooling doesnt seem to be an option. Im not entirely sure why i developed the phobia, I cant really explain it. Ive been to the doctors and counselors. Anyway recentley i started sixth form but it seems i still cant step foot properly into school without being stressed or breaking down. If anyone has any advice that would be really helpful. Im afraid im ruining my future and putting a lot of stress on my mum.