Regarding re introduction of lactose.

Good evening. My daughter is 7 mos+ and nearly a month ago had diarrhea. I was unaware of the fact that I shouldn't give her milk, so I fed her milk during that episode , 5-6 times. Similac 2. My pediatrician didn't inform me about not giving her milk.or feeding her a lactose free formula. After that she is unable to consume lactose based formula. I have been giving her Isomil , on his recommendation but I am not satisfied with how is he is handling the stuff. My daughter's condition has definitely improved but whenever I trail her with similac, she develops colic pain. Though, initially it was followed by a mucosy stool, that has stopped. But she develops this colic. I am really very tensed to how to reintroduce lactose to her. When to, kindly guide me as I am not getting any proper guidance anywhere. Thank you