No protienuria but still edema

I have minimal change disease nephrotic syndrome and recently began spilling protein in my urine which inevitably led to some edema. I had the typical frothy urine and everything. They put me on prednisone and after a couple weeks I noticed the frothy urine stopped and I also showed no protein on my urine test strip but the edema hasn't gone away and I remain especially sensitive to salt as well. Usually once the protein stops spilling the water weight falls off but this time around it doesn't seem to want to go away. The edema also worsens throughout the day as I eat more salt. In the mornings I have less edema. Why would I be holding onto water if there is no proteinuria?