Hello, I found streaks of blood in my 2-month-old child's stool for 5 …

Hello, I found streaks of blood in my 2-month-old child's stool for 5 days now. We have done a test for hidden blood in breast milk and it came back negative. I have excluded breast milk for 4 days already. Before going to the bathroom, the baby cries or tenses up, and there is also mucus in the stool. What could this be? What tests should we do? Ultrasound?