You need to see a psychiatrist for diagnosis and treatment. You are showing symptoms of depression. If you have depression, you can't get out of it by yourself -- you will need help. Fortunately, there are professionals standing by who have dedicated their lives to helping people just like you.
There can be biological causes for low mood and energy. I'll mention two.
The first is hypothyroidism (low thyroid). This comes on insidiously, with lower and lower levels over a span of years. Your energy gets lower and lower, slowly over time. Thyroid hormone is needed by every cell in your body to produce energy. Can be diagnosed with the TSH blood test (if above 3, suspect hypothyroidism).
The second is low testosterone, which can also be diagnosed with blood tests. It also develops insidiously. Testosterone has a powerful effect on the brain. A hundred years ago, testosterone was used as a therapy for depression (it worked).
Go see a doctor. You can't get out of it by yourself.