At your age it is very, very unlikely that it is ALS. But there is always a very small probability that it is, or that it is another neuromuscular disease that has some similarities with ALS. There are other neuromuscular diseases that can be treated and that have a progression rate much slower than ALS. On the other hand, in the rare cases in which ALS starts at an early age, usually it progresses much slower. (Stephen Hawking is still alive!).
Besides neuromuscular diseases, there are other diseases that can resemble ALS. If your hand continues to weaken or the weakness spreads to other parts of the body, I would try to get tested for other diseases. The fact that the weakness in your hand fluctuates, make it less likely to be ALS, but in multiple sclerosis it is common for the symptoms to come and go.
With respect to the fasciculations, you said that you "felt them" in your arm. The thing is that usually fasciculations (at least in the beginning) are no something that you feel but something that you can see if you look at your arm for some time. If you haven't done it already, you can find videos showing fasciculations in Youtube. If you don't see that on the surface of your arm, most likely it is not fasciculations. If I were you, I would try not to worry too much, but keep watching your symptoms and start looking for a doctor that might be more willing to refer you to a neurologist if your symptoms get worse.
