It is your employers responsibility to withhold taxes from your wages based on the W-4 you gave to your employer. Only your employer or the employer's payroll department can tell why no taxes are being withheld.
You may want to give your employer a new W-4.
Go to this IRS website for the W-4 withholding estimator -https://www.irs.gov/individuals/tax-withholding-estimator
