it will be entirely up to the USCIS examiner to decide exactly how many months or years worth of documentary evidence to require from you and what type (taxes, bank statements, utilities, and etc.) You will find that out during your interview. For you it is sufficient to note that you are responsible for bringing all doc proof of the last 3 years or since you got married, whichever is sooner.
Kindly be advised that the answer above is only general in nature cannot be construed as legal advice, given that not enough facts are known. It is your responsibility to retain a lawyer to analyze the facts specific to your particular situation in order to give you specific advice. Specific answers will require cognizance of all pertinent facts about your case. Any answers offered on Avvo are of a general nature only, and are not meant to create an attorney-client relationship.