What are the symptoms of depression?

I don't know if I have it, but I'm also not sure I I do. I just feel sad and lonely all the time. I'll smile and laugh, and I'll joke around and be included in things, but...I just feel like something's missing. I don't have friends over, I don't go over to friends houses, and my brother is constantly bringing me down. he's two years younger, which makes me feel even worse that I could let a little kid make me sad. My sister is perfect, my mom is...well, my mom. If you knew her you'd understand, and my dad is just an ***. The only way I feel like I can even "speak" is to write or type, and now that i'm trying to open up, everybody keeps on telling me my writing is boring. I hate. . .I hate feeling so empty, and I just feel like I need a good, long hug from somebody that really cares, but I'm starting to wonder if there is somebody out there that does. The only time I feel close to normal is when I'm holding my puppy Kiah, or pretending to be happy so much that I actually believe it, but in the end I just feel like a fool. I'm constantly brining myself down, and I'm pretty sure nobody really likes me. A lot of people say they do, but I don't believe them because I doubt anybody knows the real me, and if they did, they wouldn't like me. I'm a fat, ugly, mean, sarcastic person that is horrible to be around, and I feel so guilty that I'm hiding that but I don't want to hurt people. I'm so confused. Sometimes I feel like I just want to crawl under the bed or into the closet and hibernate all year, every year, for the rest of my life until I die, but then my selfishness takes part of me once again and I force myself out of bed everyday. I need to take care of my little dog, Kiah, but sometimes I feel like she'd be better off without me. Like I'm using her just to make me smile every now and again. I don't know. Just answer my question, I'm rambling again and this was pointless anyway....