Can my employer deny my return to work? Doctor did a fit for duty certifcate saying I could return.

Employer states the doctor was unclear and she needed more info. and as a result, I couldn't return. The doctor stated I can do light duty,(meaning no strenouous activity). My job doesn't entail doing physical labor at all. I asked her to call my doctor to get clarification, but she did not, and instead, medical records were requested. If she, Personnel Mgr. determines I have a disability, she may provide a reasonable accommodation. I have been diagnosed with conditions that are listed as ADA disabilities and I am being treated. I think I can perform all my major job duties with minimal exascerbation symptoms. I've used an additional 4 weeks off already with no pay under FMLA waiting for more documention. I may need future treatment, and if this doesn't get resolved in 2 weeks, I will likely be terminated due to exhaustion of FMLA 12 weeks, and employer's denial to allow me to return to work. Do I have a case for violation of my right to return to work being denied and other regulations being violated so I can regain that FMLA time back and lost wages?