My period is now 6 weeks late... I did a pregnancy test 3 weeks ago and the test came back negative, however, my period still has not returned... what could be the possible causes for this? What advice can you give to me?

There could be many causes from anxiety/stress to a physical problem.

I would ask my Pharmacist to recommend a HPT and use it. If it is negative, I'd call my Doctor.

Usually when you're 6 weeks late you're pregnant. Take another test and I'm sure you'll get a positive result this time.