It's all a bit of a guessing game really - the surest sign you can get is usually a missed period (although saying that you can still have an implantation bleed). Sore breasts, bloating, tummy pains, sickness, etc all used to come hand in hand with my periods some months, other months nothing. So these symptoms are not always reliable. Some women simply just feel 'different'.
If you're late do a test - it's the easiest way I guess! Your doctor can do blood tests for you to check HCG levels if the test doesn't show up positive and you are still not on your period.
HTH and good luck with the outcome you want!