Your symptoms suggest you could have a depressive illness for past 3months: Low mood, feeling down, negative thoughts, wanting to be alone, feeling helpless, low confidence, decreased concentration, regretful thoughts, losing control, purposeless, suicidal thoughts.
You probably had similar but not that severe symptoms in the past.
If you are having suicidal thoughts means now your illness is serious and severe.
Next Steps
Talk to your parents or closest person first. Buckle up and garner courage to visit a psychiatrist accompanied by them. Depressive illness is a very common treatable illness. You would definitely feel a lot better after treatment. Treatment would involve medicines or counseling(CBT) or both.
Health Tips
Talk and tell. Open up and speak out. If you have chest pain or stomach pain or even Malaria you would tell your parents or someone. The depressive symptoms are also similar. They are distress signals for suffering underneath.