Well you need imaging, there could be something causing inflammation in your left maxillary sinus like a mucocele that became inflamed with the airtravel/pressure change and traveling in Italy (lucky dog). but clearly if it stays in the V2 distribution of the nerve, and I will attach a picture to this webpage, and you say your face is swollen, even if just slightly, then I cannot implicate a stroke ( I mean, a lacunar stroke in the right thalamus of your brain could cause a pure sensory deficit on your face and left hand/arm, but it would be your entire left face below the chin to the neck) and there might also be pain.
An MRI with attention to the gasserian ganglion on the left (facial sensory ganglion) is what you need. Look for localized inflammation. Again, I cannot be certain without seeing you and an exam. One thing you could try is get a cue tip and pull the cotton out a bit to get just a hair exposed or use a make up brush with a single hair, close your eyes and try to map out the exact limits of the numbness on your face, compare it to the attached map of facial sensation and see if it fits V2 distribution (dark yellow). A Neurologist could certainly help you with this problem, there are also a facial sensory test called the blink response test done in his office to test the trigeminal nerve in that area, and he would schedule the MRI.
I hope I helped answer your question, please reply or hit the accept button if you are satisfied as that is how I get compensated for my work. thank you. Dr. Frank T.