My Employer has denied my letter of accommodation and I have caner. What do I need to do next?

I live in the state of Illinois and have worked in a nursing home setting for 10 years with this company. In March I was diagnosed with Breast Cancer and currently undergoing chemo with a mastectomy in October/November this year. I also have a port which was surgically placed. I have only missed two days, due to sickness from the chemo. I have three months of sick time coming to me that I am hoping to use after my Mastectomy. I have had excellent evaluations. Until recently, I was occasionally working on the "wheelchair" floor. Most of the time I worked on all the other floors. I can still perform all my job duties, except lifting the wheelchair people is VERY difficult, even using the lift. I have spoke to HR and given them a letter of accommodation to remove me from the wheelchair floor. This was denied, due to it being in my job description that I must lift. I still want to keep my job and I can still do my job 100% on the other floors. I have explained this to HR. My Doctor has written me a letter stating I may lift as tolerated and HR want my Dr to be more specific of the weight. However, it depend on the day and how I feel from chemo. Now my employer has scheduled me consistently on the wheelchair floor. Please help!! What can I do to keep my job? I am only 60 years old and can not get any financial help and need the insurance. HR has insisted that I take a leave of absence since I can't "do my job". This is VERY stressful!! I appreciate any help and advice. Thank you for your kindness ♥