Hello,
Delay in menses can be due to pregnancy, stress, hormonal imbalance, imbalanced diet, excessive exercise, depression, thyroid problems, poly cystic ovarian disease etc .If your pregnancy test is negative you can get a blood for Beta HCG done to confirm. If it is negative it can be due to the above mentioned causes.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
I'm pregnant so no, I'm not hehe. but I suggest u get ur betas checked since ts been 4 weeks already. a test can b wrong if ur HCG levels aren't high enuf 2b detected by the test. also, take a pink dye test if the ones uv taken before were blue dye. they tend 2b more accurate. Good luck and SSBD!