On the contraceptive pill, taken correctly. due my withdrawal bleed but no sign of it? should i be worried about pregnancy?

Correct pill usage: If you took the contraceptive pill "correctly" then no you should not be concerned. If you did not, then run a pregnancy test before starting another package.

Yes, rule it out: Oral contraceptive pills reduce your risks of pregnancy but do not prevent every woman from getting pregnant all the time. They unfortunately have a reported failure rate of 6 to 8 %. It would be wise to have a urine or blood pregnancy test ASAP and if it is negative to ask a caring and knowledgeable Gyn for an intrauterine device or a subdermal implant, which are most effective contraceptives.