Welcome to PC Plutonian - from your post it seems like you may suffer from an underlying emotional problem (like depression), since you were suicidal in high school. You're also self medicating with alcohol and drugs, which can also mess with your emotions. Another thing that's very common at this stage of your young life is - you're at a transition time. When young people are in high school, real life worries and decisions start to creep in. When the person doesn't have a clear vision of what they want to do in life, this causes a lot of anxiety and uncertainty. Basically you're scared and can't envision a direction, which is why you're so unhappy.

Its also very tough in the job market and can understand how intimidating all this is. If you do have an underlying depression, this can make everything seem like a mountain. Now that you're graduating you're probably worried about finding a job and what you're going to do with this mystery of life. Reach out to a school counselor, your dad or anyone who can guide you. I think you also need to tell your doctor about these nagging feelings. I hope it gets better and life will be an adventure worth looking forward to.