I'm having a "dark" day

Today has been rough. I feel like a miserable piece of shit who is worthless. I'm not sure why, but I suddenly have this feeling. Every so often I get like this. I have been on my meds, so that's not it. I just can't understand what's wrong with me. Everyone tells me I'm pretty and have a great smile. Why am I so lonely and miserable? Obviously there is something more... a good friend of mine just had a birthday and I told him we would grab some dinner - my treat. He agreed, but always seems to have an excuse. Is he ashamed to be seen with me? Am I really that ugly and gross? I can't help but figure it's ME with the problem... which makes me feel fat and gross... thus leading to me not eating because, god forbid, I'll get fat (ter). I automatically figure there is something wrong with me... because it can't possibly be anyone else's fault or flaw. I feel so fat & gross, but I know I'm not THAT fat... I have tried numerous weight loss pills... is that bad??? I am so depressed and hurt... what should I do?????