When you started working, you should have completed a P46, and ticked box A. This should have given you the emergency tax code of 747L. If so, then if you earned less than about £143 in a week, no tax would be deducted. If you didn't use your allowance, this is brought forward. So for the first two months of the year, approximately that you didn't work (from April to July), you should have accumulated around £1150 of tax free pay, in addition to the £143 per week.
If, for whatever reason, you did not complete a P46, or if you ticked the wrong box, you may be on a 0T W1/M1, or a BR tax code; this means that you are not receiving the personal allowance
If this is the case, then simply call HMRC on 0845 300 0627, and ask them to change your tax code to 747L. You'll need to have your National Insurance number to hand, and probably your employer's PAYE reference number (this is three numbers, a slash, two letters, and then (up to) five numbers e.g. looks like 123/AB45678) They will then notify your employer, and you will then receive the overpaid tax through your next payslip (it may take a couple of weeks for them to inform your employer, and your employer to update the records).
If you post your tax code (this is the equivalent of W-4 withholding), then I'll be able to help more, but I suspect that you're on a 0T W1/M1 or BR code instead of a 747L code.
Andrew