What week is it?
You need to push!
It's best to increase the nutrient dose for two weeks.
This is what my Northern looked like after week 4. If it's about the same week for you, you don't need to worry. If they are significantly older, you need to increase the nutrients, and very importantly, amino acids must be included to boost the buds. One more tip: even though it's not standard for automatics, Northerns like to be defoliated. So, strip some leaves. Then they'll really take off again.