Lactose intolerance?

My baby is 4 months and formula fed he takes nutramigen. He has had diarrhea once or twice a day for a month now. His doctor says its probably from the milk but she is not concerned since it only happens once or twice a day.

He is always uncomfortable after eating and seems gassy and wiggling all the time. He has stomach pain where he cries some days. Im starting to think he is lactose intolerance. He has an appt on Thursday and I will mention it to his doctor but has anyone had or has a lactose intolerance child and can you share what the main symptoms were.