If I have used my 12 weeks of FMLA and still have problems do to my illness does my employer have the right to write me up for going home early from work or still missing work due to my illness? I have Hepititus B and at time really feel sick. Can I be termed for my absences?

If you have already exhausted your FMLA you have also already exhausted your job protection. Yes, you can be written up or fired for continued absences, even if they are medically related. The law allows you 12 weeks of protected time. When that is used up, your employer has no further obligation to offer you any time off for medical reasons until you re-qualify.