Hi, I'd like to help you with your question.
It sounds like you do have some mild depression. It is not uncommon for people to experience depression at sometime during their lives. Success in life has little to do with whether or not you experience depression. It is usually about a deeper unresolved issue. If you have felt this way throughout most of your life, then you could have a mild depressive disorder called Dysthymia. Dysthymia is characterized by chronic, mild depression that appears more days than not and lasts a minimum of two years.
The best option for you is to see a counselor. While medication is a good choice if you feel you cannot cope and get through the basics everyday, it will not solve the issue that is making you feel depressed. Counseling can help you work out why you feel depressed and help you learn ways to resolve it. Sometimes, it is just the act of sharing how you feel in counseling that helps your mood lift and helps you feel better.
To find a counselor, talk with your doctor about a referral. Or you can search on line at http://therapists.psychologytoday.com/rms/.
You can also help yourself. There are several good resources about depression. Here are some to help you get started:
Beating the Blues: New Approaches to Overcoming Dysthymia and Chronic Mild Depression by Michael E. Thase M.D. and Susan S. Lang
The Depression Cure: The 6-Step Program to Beat Depression without Drugs by Stephen S. Ilardi
Undoing Depression: What Therapy Doesn't Teach You and Medication Can't Give You by Richard O'Connor
You can find these books on Amazon.com or your local library may have them for you.
Let me know if you have any further questions I can help with,