Why do I hate sharing my problems?

Yes I know, it's ironic and hypocritical of me to share a problem about sharing problems. Moving on, whenever I feel down in the dumps and I feel like talking to someone about my problems I suddenly feel uncomfortable. I know people don't like to hear people who whine so I avoid it mostly. I also hate being the center of attention (I despise it so much it's strange). Basically I feel much more comfortable keeping it all in my head. Sorry if I sounded pretty abrupt there. So my question is why do I feel worse by sharing problems and why do I want to keep it all in my head? Is this normal? Any comments (negative or positive) will be appreciated. Thanks :)