Constipation treatment. Products again!

My daughter is 6.5 months old. She was diagnosed with secondary lactose intolerance at the age of 2.5 months as she was having blood in stools with diarrhoea. Then it continued till completion of 5th month. She was exclusively breastfed till 5 months. After that her Dr asked to give her isomil infant formula and introduce other pureed foods to her. Now having isomil for approx 2 months she is passing motion once in every two days and sometimes it is hard. We are giving her bonnisan and ajwain+ saunf water as prescribed by dr. But from past 3-4 days she is crying so much at the time of meals. Everytime i fed her she starts crying and put pressure for poop but is doesnt happen and she is rejecting food and isomil. Yesterday and today she vomitted also may be due to gas. So what can be done to regulate her bowel movements. And when should we start milk products again