thank you for your query,
the fact that you are experiencing irregular periods
and spotting and also cramping is a sign of the side effects of the birth control.
it means that your birth control method is not suited for you.
these are not the signs of pregnancy
but still if you want to be sure,you can undergo a blood test
i would advise you to consult an OB/GYN to change your birth control method.
wishing you good health