you could still smell stuff even if it's a sinus headache. Doesn't mean your nose has to be clogged up. All the mucus is stuck up in your cavities. You have sinus cavities all over your face. Above your eyebrows. Under your eyes, on the sides of your head...
applying firm pressure, and gliding motions over those areas can help with sinus headaches. It may not go away at first, but it can help a great deal. And the decongestant can help all that stuff to become unclogged.
I'm not a doctor, but my mom's helped me out with this stuff all my life, and my massage class - learning facial massage has helped.
If it still doesn't go away soon, I'd still try to see a doctor.