Thanks for using the forum. I am happy to address your questions, and my answer will be based on the information you provided here. Please make sure you recognize that this forum is for educational purposes only, and it does not substitute for a formal office visit with a doctor.
Without the ability to examine and obtain a history, I can not tell you what the exact cause of the symptoms is. However I will try to provide you with some useful information.
One-sided numbness of the body is most commonly due to a problem in the brain (as opposed to other areas of the central nervous system such as the spinal cord or peripheral nerves). Many possibilities exist, and depend somewhat on your age, your risk factors, and the nature of your symptoms (whether or not the numbness started suddenly or gradually, whether it is a complete loss of sensation or a tingling, whether it is an objective finding on examination or it is only a feeling that you have etc)
The most concerning cause of numbness on one side of the body is a stroke. Please understand I am not trying to imply you have had a stroke, but only that this is one possibility. Strokes occur predominantly in people with risk factors: smokers, high cholesterol, diabetics, hypertensives, and people over the age of 55. However, they can occur in any age. If your numbness was due to a stroke, it would start somewhat suddenly (over minutes) and would likely persist without significant improvement.
Other potential causes include multiple sclerosis, a brain tumor, a vascular malformation and others. Transient one-sided body numbness (lasting for example for minutes up to 30 minutes then resolving) could be due to a migraine (the aura of migraine, in which case following the numbness, a headache occurs) or seizures.
Since your numbness has persisted, I agree an evaluation by a neurologist is warranted. It is reassuring that your MRI did not show stroke per your statement. It would be very useful to know the DWI and ADC results if they were available. Also, hopefully, the lumbar puncture had demyelinating studies performed such as oligoclonal bands, myelin basic protein, and/or tourtellotte’s.
Thank you for this opportunity to answer your questions, I hope you find the information I have provided useful, good luck.