I possess forgetfulness, sometimes it causes embarrassment, i want to ask what are its reasons if it is in this age?

TB medications?: At your young age, dementia is not a concern. Many people have this problem and do not have an identified cause. Some have attention deficit disorder (with or without hyperactivity). In your situation, certain TB meds (isoniazid) may be associated with central nervous system side effects . I recommend discussing this problem with your doctor.

Inattention, maybe: Emotional troubles such as anxiety/depression are common reason for folks to not remember things. Attention deficit disorder is another common reason. Two subtypes--hyperactive and inattentive. The inattentive often gets less medical attention, but this can be/likely cause of your trouble. I advise a visit to your doc for assessment. Good luck.