What should I do?

Due to your illness i believe 你 have a practice nurse at your disposal? Use her knowledge. Go visit her and ask if what they are doing is right.
Demand to use the lift as 你 are classed as disabled and it is there for your use, offer a compromise, 你 will work up the stairs one classs, use the lift 下一个 and do forth. They need to give 你 rest periods also. It could be wise for 你 to begin and leave classes 5 分钟 earlier then other students to give 你 time to get up and down the stairs and also avoide the rush of students that could seriouly damage 你 if they don't take care.
你 could also go to a junior legal system and ask for a half hours free trial and ask 问题 about legal action towards the school if 你 are damaged 由 climbing the stairs and if 你 think they have any legal audacity to say such things (you need to climb the stairs, lifts are for disabled people,due to health and safety etc)

But first and foremost, talk to your doctor/nurse and ask if climbing the stairs will actually make 你 better 或者 worse. 你 never know, strengthening your legs 由 climbing the stairs at school may make it easier for 你 to walk , and you'll have to grin and 熊 the pain for that achievement.

First:I'm Srry about your walking problem.I hope it gets better.Second:Either 你 need to be homed schooled 或者 你 need to tell your parents and your school that 你 are in some serious pain.You need to make them believe you.Making 你 climb the stairs;now that is just mean and stupid!! I can't beliven people will make your pain worse!!Oh,sorry
I was off subject!Like I 说 tell them that 你 are in some serious pain.Your parents may have to fight back on the school.A lot I mean a lot of parents do that.I hope this helped you.

its your right to be able to use the elevator specialy after 你 have told them of your pain. it would also get 你 to the class with less ease and energy, and quicker. and all 你 want is to focus on study, and not the pain associated with it. whether 你 see a local mp, 或者 even put it in 写作 to the school board, your voice should be allowed to be heard.least 你 说 something. and safety reasons? and if 你 fall upon the stairs, as 你 struggle. 或者 will allow 你 to have to;have a fall. shake a leg dont break it, good luck, hope the school does what is right for one of their novices;-]

ohh u poor thing! u shud stand up for ur rights uh... metamorphic-ally i mean.
if u r in a wheel chair, then ppl shouldn't be forcing u to climb the stairs! i mean u can't WALK 4 God's sake! u need to convince ur parents and teachers. maybe go c a physiotherapist, and ask him/her for help and backup.

Sounds like your parents need to have a conference with the school. Get your parents alone and let them know of the problem. Ask of them for a little support so 你 can talk to the Principal 或者 whoever is telling 你 no with 更多 confidence.
And if they really 说 it was just for disabled people. I would consider that dicrimination if 你 are really walking disabled.
Let them know that in the long run, walking up the stairs can hurt 你 and them. Seeing a doctor could help. They will most likely give 你 a note saying pretty much use the lift until further notice.