Hi,
I think I understand how worried you are and I'm sorry you are going through this.
MS is very rare in people your age. It can begin tha early but very rare from what I know.
Did the fatigue and weird feelings begin after you started reading about the symptoms.
I can get worried about symptoms and my body will create all kinds of feelings that can last for a long time from worry and anxiety.
Can you describe the weird feelings in your legs?
Is it numbness or weakness, tingling? Do the feelings come and go or are they constant?
The CAT scan would not show MS lesions. You would need an MRI.
If you can first try and calm yourself because it would be unlikely that you have it and also even if you did, the fact that your cousin passed away from it at 21 is awful but extremely rare. Most people (85%) or so with MS can expect a normal lifespan .