We are not professionals on this site, but I have to say you sound very depressed. Have you seen a doctor/psychiatrist? It might help you if you sought counseling. I am a constant worrier too. My mind gets locked onto one thing and obesses about it, then will hop to another. When it does this I can't concentrate on anything else. I take a medication to curb this tendency and it really helps, which is why I suggest a doctor might could help.
Gayle