Positive ANA now Normal

My 7 year old son started with a GI virus (vomiting and diarrhea) for 1 week.  He lost a total of 4 pound in 6 days.  On 7th day with V/D gone he had hand, feet swelling.  Hands were approx four times normal size.  I took him to MD who suggested nephrotic syndrome, or minimal change disease.  Drew labs CBC, CMP negative.  C3, C4 and ANA positive.  Urine showed trace protein.  Swelling went away.  We were told looks like Lupus.  All test were redrawn.  ANA negative, CBC negative, CMP negative, Urine negative, C3 normal, C4 low.  MD has no answers.  Any ideas.