I have had weakness, numbness, & tingling on my right side (arm, leg, face) for about 2 months. Brain & spinal MRI came back normal. What could it be?

I would be willing. To bet that you are severely deficient in b vitamins. Commonest cause today is sugar in all its different forms. This is so common that my answers all seem to be the same. Alas, americans have forgotten how important diet is and the "right" food is too expensive for many. We are "shooting ourselves in the foot".
Consider these: If this is intermittent, could be due to a migraine equivalent aura, and perhaps this is "classical migraine". Rarely, multiple sclerosis is missed on standard mri's, and flair or dir approaches, or even spinal fluid analysis could explain. This can be elusive early on, and many different disorders could be playing a role. Believe you can uncover with a knowledgable neurologist at your side.