If you haven't seen a rheumatologist you should do so. Treating your lupus will also treat your kidney problems. You should also see a nephrologist if you think you have kidney involvement. Do you have any blood in your urine? Is it very frothy? That is a sign of protein in your urine (proteinuria). I had it but once treated my kidneys have been ok for the past 9 years.
Make sure all your doctors talk to each other. Don't hesitate to get a 2nd opinion particularly on treatment.
Lupus is usually treatable and most live a normal life. Some cases are more difficult to treat but the longer you wait the more difficult it is to get your immune system under control.
MCTD (SLE Lupus, polymyositis, scleroderma). Diagnosed 2005. Kidney, liver, GI tract, dysphagia, raynauds, barretts esophagus, quadriplegic in 2005. Recovered and now active in downhill skiing, golf, hiking. Meds: amlodipine, benezapril, omeprazole, potassium, folic acid, vitamins, maxide.
Remain Optimistic and you can overcome.