It is common for a nose to be hard and stiff after a rhinoplasty surgery. 18 days is a very early stage in the healing process, so it is quite normal for your nose to be hard and stiff. The tip is usually last to soften and lose the swelling, so it may take up to a year and sometimes more for your whole nose to feel soft and normal to you.
Hope this helps
Ali Rıza Öreroğlu, MD FEBOPRAS European and Turkish Board Certified Aesthetic, Plastic and Reconstructive Surgeon Istanbul, Turkey