Hi, Thanks for writing in,
I don't know on which contraception
you are on but all methods do have some failure rates. You should not exclude the possibility of pregnancy
just on the basis of an irregular period as this may occur even if you are pregnant.
I think you should take a pregnancy test, preferably a blood pregnancy test to rule out the possibility of an abnormally sited pregnancy, as you are having trouble on your left side it could be a tubal pregnancy on that side & this differential MUST be excluded to save you from any catastrophe.
I suggest you carry out a trans-vaginal ultrasound
scan as well, this test will make it easy to differentiate the causes of your pain.
If any time the pain is sever or you feel faint you should rush to a hospital.
You may send me your reports for evaluation at email@example.com.
Wish you good health.