I am in sever pain due to a spine injury & my employer is not wanting to work with me. Can I be fired for tardieness or absence before my FLMA starts?

I suffered a severe injury to my back however, I have been attending the local pain clinic and doing my job to the best of my capabilities. My manager took off a whole month earlier in the year due to a non work related injury. However, now that I have become injured and in need of medical services my employer is not willing to work with me on tardiness or unplanned absences due to the extreme pain (I birthed my child with no medication and this is by far the worst pain I have ever felt, much more than child labor.) I have been threatened to be terminated by my employer on more than one occasion and am now in fear that I may lose my job, and my benefits package that I am relying on to help me pay for my spine surgery later in the year.