Stress has been suspected as a possible trigger of lupus and other AI diseases but that is not the same as a cause. Our genetics probably predispose us to a susceptiblity and stress, injury, drugs, cancer, or infection trigger the auto immune response. Many lupers will tell stories of how stress can trigger flares so I believe there is a great deal of validity to it. Your doctor is probably correct about
what triggered your lupus but there was an underlying problem before that.
I have mctd which is lupus, scleroderma and polymyositis and have been warned by my doctors to not overstress myself physically or emotionally. So far so good. In my case there were no obvious triggers and it is anyone's guess as to what triggered an extreme case of mctd. Lupus hit me hard and polymyositis almost killed me.
Until researchers understand the underlying biochemistry of lupus doctors can only guess at what the actual cause is. Seems like it is obvious for some and for others like me, not obvious at all. I went through several years of very high stress but that was many years ago and it is possible that was a trigger. However, the only signs for 15 years were low platelets and mild anemia. The first obvious flare came 2 years ago, many years later. All conjecture.
Focus on getting effective treatment and take all the stress you can out of your life. Worrying will not make you better but the opposite. Life with lupus can be good if you get it under control and learn what you can and cannot do. My life is a "new normal" and not the same as before but good nonetheless. Adaptation is a normal part of life...it is just that lupers are forced to adapt to something other than normal aging and health problems.
Hope you can find some answers but if not it is more imporatant to find peace within yourself and make the best of life.
Bill