I am having severe depression and thoughts of suicide. I have devolved an increasing sickness, it isn't just sudden. What do you think the cause is?

Depression. It is difficult to name a cause without knowing you but often times depression is driven by a negative self voice. Finding the origin of your old view of yourself and having help to see yourself accurately can be very helpful. Consult with a mental health professional who can help you accomplish the above and you may free yourself from your suffering. Best wishes.
Get Help. National suicide prevention lifeline 1-800-273-talk (8255): please find help --- go to the nearest emergency room or dial 911. They will do a complete eval at the er. Nobody can tell you the cause over the internet. It's something that has to be discussed face-to-face. Also, involved adult that you can trust to help you get through. Good luck!