I'n not positive I can help, but I'm going to reply anyway.
Your post title was about sinus infection, but quickly morphed into trigeminal neuralgia. This is a condition seldom discussed around the water cooler, unless you're a med student, so I have to wonder where you came up with this possibility.
You said the area under your left eye "hurts," which leads me to suspect a possible sinus infection. This sinus is called your "maxillary" and we have one below each eye, actualy right on top of the cheekbone. These sinuses drain secrections from our nasal passages and if, for some reason, they become blocked due to fluids or sometimes polyps, we get a nasty sinus infection. Sinus infections are not fun and they CAN be painful. Sinus headaches are common as is pain upon bending forward which increases the pressure, they make it very difficult to breath and can put pressure on/around/near our eyes, Altogether a miserable condition.
If you had trigeminal neuralgia, which is a nerve rather than a sinus, it would do far more than "hurt." The most common descriptions of the pain of TN are SEVERE PIERCING LIGHTENING-LIKE FLASHES OF EXCRUCIATING PAIN.
This pain can be brought on simply by touching the trigeminal nerve.
If you are not having this type of pain, you should consider a head cold or a sinus infection........both possibly exacerbated by allergies.
I can't tell you what this pain is from. See your doctor, who WILL be able to tell you exactly what it is and treat it.
Sorry if I wasn't able to help.
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