I don't really know if I belong on these forums, I'm not diagnosed with depression

I'm really just wondering if I'm just being silly, or overstressed or something, or if there's something more going on.

The first thing that brought me here was that in the week September 21 I freaked out about a few things.. around that time. At one point I was in my room, and I was shaking because I was upset. Mostly though i've just been sad. I'm not enjoying things at all anymore, many of which I really used to. I don't feel like talking to anyone.
I can be a shy person too... I normally don't talk to people they talk to me. I've thought a lot especially about my career choice and perhaps thats a main issue. I play the cello, go to college, and am now 19 years old. I've never considered myself a "good" cellist although I've gotten into a top school and should be happy, because my teacher is great and I'm learning a lot. I dont really like hte way I sound; that is a source of frustration and I almost want to stop fighting it. But besides cello, I'm not really having fun here. Activities I used to enjoy now just bore me, but I dont feel like doing anything else either. I feel run down a lot, despite the fact that unlike many students here I generally get at least 7 hours of sleep.

This morning I woke up, got over to the practice rooms, hit a pathetic 25 minutes in there. I went back to my room because I felt like crying, as I often have lately, but as always I didn't cry. I ended up sleeping through the morning ( and this mornings class) because I just couldn't get myself to go. I should not have been tired because I got 7 hours of sleep AND just had vacation.

It could be just that I'm lonely at times, or that I'm discouraged by some aspects of school, but I've been feeling disinterested and a dull sadness for at least 2 months now, before that wasn't that great either.
Advice of any kind?
I'm sorry this post is really confusing.