Well, simply having pain behind your eyes and feeling dizzy is not a sign that you have MS.
Sometime people with MS develop pain in one eye -- which is called optic neuritis. But not typically pain behind both eyes.
Pain, sensation abnormalities, weaknes in the limbs or body are other common presenting symptoms.
You do not sound as if MS is a concern.
If the symptoms were concerning, then the next test would be a MRI of the brain.
But if you have been evaluated by several doctors and told you have sinusitis - then you probably have sinusitis.
An optometrist can check the clarity of your vision, but they really are not trained to diagnose things like optic neuritis, though they certainly can tell you if that is a possibility.
Not having optic neuritis does not necessarily rule out MS. This is because people can present with any number of different symptoms.
And if your doctors don't want to send you to a neurologist, in their clinical judgement they feel your symptoms are not MS. Certainly, if your symptoms worsen, or become more like MS - a MRI of the brain should be ordered to evaluate this.