What kind of doctor are you seeing tomorrow? If it's not a rheumatologist, then be sure to ask for a referral to see one. They are usually the only ones to make a diagnosis of lupus when there is negative bloodwork. Other ways to get a diagnosis with negative blood work is through a positive biopsy (of skin or kidney if there is kidney involvement). Only rarely will a diagnosis be given with only symptoms but zero positive "proof" via bloods or biopsy.
I would be sure to mention the fact that lupus runs in your family, with two sisters already diagnosed. It helps to bring a symptom list to concisely state what the issues are for you (helps to make sure you don't forget anything). A medical history list might be helpful too. If the doctor still feels unable to make a diagnosis of some sort, don't give up. It can take a while for bloodwork to turn positive, but there are expert doctors out there willing and able to diagnose and treat suspected autoimmune diseases (often with the label of UCTD - undifferentiated connective tissue disease). The treatment for that is often the same as that for non-organ involving lupus.
Do you know exactly what blood tests were already run, and what the values were? If possible, try to get actual copies of the blood test results.
Good luck at your appointment.