Foods that cause constipation

I never thought I would need to ask this question but here goes. My 2 year old has had diarrhea for over a week. Took him to the doctor and they were not much help. She basically told me to cut milk out and limit fruit. I’ve done that over the weekend and yet he’s still having watery stools. He explodes through the diaper and onto an outfit a day pretty much. It’s to the point of me having to throw him in the tub and just spray him off and then bathe him. It gets everywhere. I don’t know what’s causing it at this point. He hasn’t had milk since Friday and very limited fruit. He will not eat bananas. They told me to just feed him starchy foods but it’s not helping. He only drinks water as well.

He only has had water since Friday.

We assumed he could be lactose intolerant but she ruled out a stomach bug as it’s been going on for 7-10 days at this point. He’s taking fluids just fine and his vitals are fine as well so she didn’t suspect any dehydration or anything. He just will not eat certain foods but will take his normal amount of water so we are good with that.