you have not mentioned your sons age.
Most of the childhood nephrotic syndrome
are benign and respond to steroids.
Your son has again developed proteinuria
, so he is probably in relapse. Check proteinuria again for next two days . If it remains >1+, he again requires prednisolone
You may require to continue prednisolone for long period of time or another immunosuppresive medicines.
If relapses are more frequent renal biopsy
may be required.
Consult your nephrologist