What's wrong with my puppy?

My puppy (14 wks, Australian Shep-Poodle mix) was hospitalized for one night due to vomiting, diarrhea, and shakes/seizures that lasted about 10 hours. We did not know whether he had ingested any toxins and preliminary blood tests showed okay sugar level, no lead, and he had no fever. He was given valium and steroids and calmed down after the steroids. He is home now but we still don't know what caused his attack; also he is having frequent urination, unable to hold it in and has peed inside several times, and a urine test today showed some protein in the urine. We are still waiting from results from a blood test sent to another facility. Do these symptoms sound familiar to anyone at all? So far, our vet is stumped.