Can I be fired for being sick even with a doctor's note?

Hi all,

I contracted a viral infection and have been very sick for the past week. I work part-time, so I only missed 2 work shifts as a result. I also have a doctor's note to back it up. However, the schedule for two weeks out at my job was posted online and I'm not on it.

I found coverage for both shifts that I missed, and was sent home from one of them by the business owner himself. Am I being fired for being sick? I can't afford to lose this job right now. Can anyone offer advice? Is there anything I can do?

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