You may take up to 12 weeks off, to care for a parent, within a 12 month period, assuming you meet all other eligibility criteria, under the FMLA or CRFA. The employer may ask for certification from your father's health care provider as is reasonably necessary. Good luck to you.
FMLA does provide you time off in each 12 month period. In addition you should check your employee manual that may provide additional benefits over and above the FMLA statute. You employer does have the right to documentation, however if you are retaliated against or have unwarranted changes in your employment after you return, you may have a cause under prohibited retaliation or harassment. You can contact the Department of Fair Employment (and perhaps should visit the website) to consider whether you are being treated unlawfully. In such event you may also contact an attorney several of whom will offer a free initial consultation. Good luck to you.