Feeling low, not interested in activities which were previously pleasurable, having negative thoughts about almost everything leading to worthlessness, hopelessness, helplessness and intent to end one's life are all symptoms of depression. From your description it seems like you have these symptoms. No matter what the reason for such thoughts could be, it warrants a consultation with a Psychiatrist as it poses significant threat to one's life.
Next Steps
You should consult a Psychiatrist at the earliest.
Health Tips
Always keep someone by your side. Any thoughts of self-harm are momentary and you shouldn't act upon them. I repeat, consult a Psychiatrist at the earliest.