I believe you should be protected but am not 100% sure. it seems since the employer was aware of the medical condition and it was documented the extra 2 days might not have been such an issue.

unless of course there were issues prior with absenteeism, etc. I would offer them ample proof you were indeed hospitalized and unable to return to work for those 2 days. if those days were required by medical professionals include that as well. perhaps they think you were just extending questionable leave.

what type of work is it?
you had only been employed 2.5 months.
you asked for a week, which got extended to 10 days per a counselor (someone you see regularly? psychologist, social worker, exactly what type?)
did you provide documentation?
then YOU called work & requested 2 additional days. is there a dr request?

that is a chunk of time for only being employed a short time and if there is NOT decent documentation, just phone calls etc, you might have a difficult time.

is there a union?

do some research on the American with disabilities act to check your situation to see if it meets the criteria.

good luck. I wouldn't resign. make them fire you. but make sure you have all documentation is correct, valid and accurate. know also, if you fight and win, work might also not be a pleasant place to be.