Sounds like the Advocate is working, but if he was wormed a week or so ago I think it might be worth phoning the vet to ask if it's normal to still be seeing worms this long afterwards. I don't know the answer, but it might be worth asking the question
If you've only increased Harri's food slightly he may not be getting enough now that he's quite a lot older. How does he look? When you look down on him from above can you see a slight waist behind his ribs and when you touch his ribs can you feel them without pressing hard? If he has too much of a waist and you can quite easily feel or see his ribs then he may need more food. It's quite hard to judge though, as all pups are different and the guidelines on his food packaging are just that, guidelines.
He will probably change shape quite a lot over the next couple of months as he continues to grow upwards and may go through gangly looking stages until he's about 18 months or so and matures physically.