Welcome to the forum! Sometimes new posts get passed over when introduced in another thread so I started a new thread for you so more people will see your post
I'm sorry you are having problems so young. There are certain criteria for a diagnosis of MS, and your neuro doesn't feel that you meet those right now, and wants to wait and see what happens. It is true that in some cases people only experience one relapse, but if you do experience another relapse and/or have another MRI in the future showing more lesions that might be enough for a diagnosis.
I've yet to see any diet or supplements that help with MS symptoms. Some supplements actually boost the immune system which can be harmful for MS patients, so please be careful. There are many medications though to help with symptoms, and you may or may not experience those side effects that you seem to be fearing will happen. Everyone is different in response to meds, you might find one that works for symptoms that you can tolerate well. Best of luck and please keep us updated as to how you are doing, I'm sure others will be along soon to welcome you.