Hi there, have you had Dougall checked by the vet to see if there are any underlying reasons for him being itchy?...fleas, allergies etc? Does his skin look inflamed, sore or flakey? I wouldn't change his shampoo too often as this may just make the itching worse. Find a good shampoo with tea tree, or something that soothes the skin in it and use it weekly and see if it makes a difference before swapping to another. Also, don't rub him too vigorously when you bathe him as this may also add to the problem....massage him, rather than rubbing. Make sure you rinse him thorougly as any shampoo left on the skin will cause him to itch too. Brush him while he is still damp from being washed as this removes more hair and stops it flying all over the place too

You can also damp him down with a cloth before his daily brushing to catch more hair. As long as his coat is healthy and not coming out in clumps these are the only things I can suggest other than seeing your vet or perhaps talking to a dog groomer for some tricks of the trade? Best of luck