Three weeks fading is within the normal range. The smell is off gassing from the foam and the packaging, and most of it goes in the first few days, with a long tail after that. Mine took about a month before I stopped noticing it, and I only noticed at all because I was looking for it.
What actually speeds it up is airflow across the surface, not time. Strip the bed, stand a fan blowing across the mattress for a few hours a day, and keep the window open. Heat helps too, so a warm room with airflow beats a cold room with airflow.
What does not help: covering it with a thick waterproof protector immediately, which traps the smell in and slows everything down.