I need some guidance/advice/thoughts.

Hey everyone, I’m Souiii and I’m 22 years old in the UK. Bit of history, I have been having lots of issues with my arms for the last 6 months where they are numb, feeling almost dead but not quite? Sometimes lose grip in my right hand and it shakes also on occasion. I’ve had a nerve test done in my arm and it came back normal, since the GP said it was Tennis Elbow but I am not convinced. I have followed what the GP suggested but it doesn’t seem to be getting any better. Also, on occasion my arm jerks and I’m sure it wouldn’t do that with Tennis Elbow. My grandad has MS and I have spoken to him about my symptoms and prompted me to try and get in again to see the doctor as he felt the same before he was diagnosed. I have an office job, but have made sure I have the right posture, mats and a proper keyboard to prevent injuries that come over time. My vision seems to have detiorated a lot over about 2 years, my balance is shocking, I’m so fatigued and I feel like maybe the doctors are not taking me seriously. Maybe someone can give me some advice on what to do next. It just seems to be getting worse but because I am so young and usually fit and healthy the GP is just fobbing me off. Thanks, Souii