Membraneous nephropathy is a relatively common cause of kidney disease that results in large amounts of protein in the urine. It is form of glomerulonephritis and requires a kidney biopsy in order to establish a specific diagnosis. The Mayo Clinic has an excellent web site on Membraneous Nephropathy and I suggest that you review this information at: http://www.mayoclinic.org/diseases-conditions/membranous-nephropathy/basics/symptoms/con-20026050
I also suggest that you review this information with your nephrologist. Your nephrologist is best trained to suggest the proper treatment and establish a prognosis for you with this disease.
On our web site, we have a shorter review to glomerulonephritis including Membraneous at: https://www.kidney.org/atoz/content/glomerul