Why do i have a complete lack of emotion?

Depression: It sounds like you may be suffering from a depression. Depression can result in feeling a sense of low self worth, anhedonia, and can manifest itself in the form of suicidal or homicidal thoughts as well. Clinical depression should usually be treated with meds. You may also have low vitamin d, low vitamin B12 levels, anemia, hypothyroidism etc. Go see your doctor and get a formal evaluation.

Trauma?: One symptom of post-trauma stress disorder is numbing or feeling like one doesn't have any feelings. Another possibility is that growing up you did not receive the psychological space to have feelings as a child and consequently you don't know what you are feeling. This can also be a side effect of medication or being in shock from a loss of a loved one/ grief. Some ideas to consider.

Emotion: Emotional numbing can occur often as a response to extreme trauma. An example would be a combat veteran returning home and feeling nothing at the death of a loved one. People with schizoid personality disorder are indifferent to interpersonal relationships and appear to be emotionless, often. These are just two examples, there are others.