My interests are do to the misdiagnosed illnesses of my father, which is the field of Medical Coding and Billing.
>> "do to" = ???
>> "misdiagnosed illnesses" = "the field of Medical Coding and Billing" ????
This sentence needs major revision. For one thing, I think you mean "due to," right? No spell checker will pick that up because there's no spelling error; it's a word-choice error. In addition, the word "which" at the beginning of that relative clause seems to refer to "illness" (I hope it doesn't refer to "father"!!) -- but I doubt any illness is the same as the "field of medical coding and billing," right? Also there should be no capital letters here except at the beginning of the sentence.
My father had cancer, which was misdiagnosed by a doctor at Stanford Medical Hospital. Its formal name is Stanford Hospital & Clinics. http://stanfordhospital.org/
He was told he just had an infection which required an I.V. of antibiotics for several weeks. My mother was told by the doctors of this diagnose.<~~word? She thought it was wrong.<~~Combine those last two sentences. http://grammar.ccc.commnet.edu/grammar/combining_skills.htm
The diagnose<~~word? was documented and with incorrect coding, years later, we discovered this.~~<This sentence needs rephrasing to be smoother and to have the ideas connected more logically.
There are similar errors throughout the rest of the paragraph. It's not a terrible paragraph, but it's rough and needs smoothing out and correcting if you want it to be an example of polished writing.
Use the following links to help you find errors and how to correct them. Then revise your paragraph and repost if you would like someone here to check it for you.
http://grammar.ccc.commnet.edu/grammar/possessives.htm
http://grammar.ccc.commnet.edu/grammar/plague.htm
http://grammar.ccc.commnet.edu/grammar/capitals.htm