Loose motion in 4. 5 months old baby.

My baby is born premature , now 4.5 months old. He is on exclusive breastfeed and is having loose motion from last 10 days. For first 3 days it was watery. We consulted doc, he gave bifilac gg twice a day and Z n D once daily 0.5ml Now stool are not watery but still loose and seedy and have bubbles sometimes. Stool frequency in 24 hours is 3 to 6 times. Baby's 1 jaw on each side is also showing up. We got stool test done and it shows ph 6 and reducing substance positive . Now doc has suggested to stop breastfeeding completely and give formula milk which is lactose free. He has no other symptoms, is active and gaining weight steadily. Current weight is 6.3 kg. Please suggest if breastfeeding should be stopped or not. Are these loose motion because of breastfeeding or teething.