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 your doctor.
Without the ability to obtain a history and examine you, I can not tell you what the cause of your symptoms are. However, I will try to provide you with information in general about what your symptoms could be due to.
It sounds like you have numbness on the left side of your body. Since you are 18 years old, a small stroke (possibly in the area of the brain called the thalamus) would be a very unlikely cause of your numbness, but in general this is one potential cause. If you have an associated headache, another possibility is that your symptoms are due to migraine. Another cause in general of one-sided numbness is multiple sclerosis, a problem with myelin, a substance that lines our nerves. I am not saying I think you have multiple sclerosis, only that it is a possible cause. Another possible cause is a localized problem in the upper (cervical) spinal cord.
As you can see, there are several causes of one-sided body numbness. It would be best for you to be evaluated by a neurologist who can examine you and decide if you need further work-up such as an MRI or other investigations.
Thank you for using the forum, I hope you find this information useful, good luck.
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