My baby is 17+3 and is only 13lbs (5.90kg). He has dropped from 50th percentile to 25th to just below the 9th. I'm doing combination feeding and although he's not losing weight, he is struggling to put weight on. He has a slight tongue tie and I feel this could be causing feeding problems but because I don't have nipple damage, I've not been able to get referral to feeding clinic to check if it needs snipped. I'm worried his lack of weight will affect his development. There seems to be support for breast feeding but nothing for formula. Someone suggested a higher fat milk but I've not heard of this. Any advice?