There are a variety of reasons you may have difficulty identifying or expressing emotions, we call this alexithymia.
One reason might be growing up in a home where emotions were not allowed or encouraged. In that type of environment, the child does not have an opportunity to learn about their emotions. There are not experiences of them having a feeling and their caretakers naming it for them and helping them manage it.
Another reason might be because you are so shut down inside that you are not aware of the physical or mental experience of emotions. This is a form of disconnection that we might label as dissociation. As a child you may have learned that emotions are dangerous, and this learning might have happened well before verbal thought has been learned. This would make it difficult to be in touch with your emotions, or have words for them or be able to explain how you got stuck in this.
And another reason it might be difficult to know what you are feeling is due to trauma. If you have experienced a trigger, at times when the brain perceives life or death danger, then the part of your brain responsible for language may go off-line. In that case being able to verbalize, even to yourself what you are thinking or feeling may be quite difficult.
Regardless of the reasons you may not know how you feel, your feelings are valid and you can learn to be in better touch with them or be able to learn how to communicate about them. Therapy can be a big help with this learning process.