Can I get fired for asking to much unpaid time off?

Hi I was wondering if I can get fired for asking too much time off I have 2 kids and have asthma specalist eye specalist neurolugist and allergy specaliat . Mind you they still have their primary dr appt I was.advise that I can get occurences for asking for too much time but its unpaid and the excuse was that they have no one to cover.my shift when i ask fir this time I do have fmla but thats for my sons eye specalist im wondering if their finding any excuse they have over 400 ppl .and I always bring my excuses what can I do