I have an odor coming from my shower drain which is on a slab. I can feel air blowing up from the drain. Is this a lost water seal and if so how do I confirm and correct

Is this shower in daily use or is it not used much? Sure sounds like a lowered trap seal. And gurgles when you flush or drain? I want you to remove the strainer and shove a stick down to the base of the trap and tell me how much water's on the end? Back to you, Tom