Lactose intolerant

So my son was on aptamil ready made when we was in hospital (I had to stay in for 2 days due to issues with myself) when we left we changed him to aptamil formula which he then became constipated so we tried colief which relived him a bit then we changed to mamia which help massively. About 2 weeks ago his poo changed to a dark green with bits we then spoke to the doctors who advised sounds like lactose intolerant.

We then changed him to aptamil lactose intolerant which changed his poo back to yellow and more loose however 2 days ago it’s gone back to dark green... I’m thinking to try him on SMA lactose free? Has anyone else had these problems?