I would say a good place to start is here on this site. They have good information about things like major depressive disorder. None of us here are doctors and can only tell you what we know from our own experiance. What you are describing sounds like depression. There are some symptoms of depression that a doctor would look at to determine if that is what is happening for you. As for bipolar, there are also symptoms of mania which is an excelerated state.
The thing with depression is that it is not based on the reality of your life. You can have a great life and still be depressed. That's because depression is an illness and not imaginary. The illness is caused by the misfiring of the nervous system, causing a biochemical imbalance in your body. Depression and bipolar disorder are very real illnesses even though they appear to be "in your head" they are not.
I would say look at the site here and maybe take a "self-quiz" on depression and bipolar, print the results and take them to your doctor. A psychologist or therapist can help you with talk therapy, but for best treatment with medication, a psychiatrist is the person you want to talk to.
I hope that helps. :)
Just from what you've said you sound very depressed. PLEASE see a doctor or someone who could help you. But if you have EVER had any signs of mania (racing thoughts, hyperactive, wild behaviour (not just from alcohol!!) you need to add that to the mix. Too often women get diagnosed with depression when they are bipolar. Make sure you give your doctors the whole picture, because anti-depressants alone won't fix a cycling mood (which is a little bit what yours sounds like) but yeah, def. get a professionals opinion soon!! Go well.