I can relate
I'm a 56 year old woman with a large port wine stain on my face that has become raised and marbled over the years. I had many laser treatments (years ago) while I was working (now retired) and took weeks off work because of swelling and difficulty putting my make-up on over the swelling. I worked for a federal agency that was understanding, and I used my annual, sick, or unpaid leave for the treatments and recovery. It always amazed me how the doctor would tell me the recovery was nothing, and I could be back to work in a few days when this was far from the reality.
Of course, none of my comments answer your question about applying for FMLA for intermittent leave for treatments. I am sure you have research the subject and it might even be worth seeking some legal counsel to determine if this is a viable option.