Can I be terminated from my job due to a side effect of a medication that I am on even though I have provided a doctor’s note?

You may not have anything you can do, unfortunately:

1) If  you don't have an employment contract, you are an employee at will; an employee at will may be termined at any time, for any reason, except those reasons specifically prohibited by law  (for example, illegal racial or sex-based discrimination).

2) A doctor's note, as a general matter, has  no legal power over an employer--the doctor is not an executive or representative of the employer, and has no right to change their employment policies or job descriptions.

3) Except as set forth in 4), below, an employer  may terminate someone who violates workplace rules, cannot do his or her job, misses time from work (or takes excessive breaks), or has poor performance, even if such is caused by medication or  medical condition. The law does not generally require employers to employ or pay people who can't effectively do their jobs.

4) The only exception is that IF your underlying medical condition qualifies as a disability, then under the law, the employer may be obligated to make "reasonable accomodations" for you. However, this doctrine is very limited in some significant ways:

a) Most medical conditions would not be considered disabilities for this purpose. To be a disability, the condition must have a significant impact on normal life functions and must not be readily controllable or curable.

b) A reasonable accomodation is a change in how the job is done, or the provison of some assistive devices or technology, which is not too costly or disruptive. If there is no reasonable accomodation, the employee may be terminated. So, for example, if your job is incompatible with frequent bathroom breaks, then even if you have  a disability, the employer may be legally able  to terminate you.