Poop looks normal for the age. Just ensure he remains well fed/hydrated with the milk and that his activity level is normal. If there's something out of the ordinary, you can bring him to see a doctor. Flies carry quite a lot of germs. Would be good if you could place food covers over your bottles and accessories to prevent the insects from coming into contact with them
Normal. Quoting my PD...”so long as the poo color is yellow, it’s OK”