My period is about a week late and i'm feel feeling right side pain and lower back. my breast usually be sore but is not this month?

Late period?: First of all, make sure that you are not pregnant by running a pregnancy test. If negative, your age of 40 indicates that your frequency of ovulation is decreasing and estrogen only cycles are more common. This may cause a delay in your period as your body is adjusting to future ovarian cessation.(menopause).

Check pregnancy: Check a home pregnancy test first to make sure your period's not late due to pregnancy. The pain could be pre-menstrual, some Ibuprofen can help. If symptoms continue, then consider seeing a gynecologist to address all of them. Best of luck.