Uti in 5 year old son?

Victoria • Married 10 years. Mommy to James and Jack 💙 pregnant with #3 due October 24th

I took my son to the doctor bc he told me it hurt when he peed and i noticed blood in his urine. They found blood and protein in his urine. He is on amoxicillin for a UTI but the protein in urine is making me nervous... has anyone experienced this?