I Feel Really Down. Well... I Feel Really Down But

I feel really down. well... I feel really down but I can be really happy at the same time... does that make sense? I feel as though I'm becoming more and more irritated, and I don't feel I can trust anyone. I'm so confused.... i'll sometimes cry over the smallest things, and within the next minute i'm able to have a laugh and a joke. I feel super stressed out and worthless - I just don't understand what's going on?! :(