Are Dark Periods, Stomach And Backaches Side Effects Of Morning After Pills?

i had unprotected sex with my boyfriend about a month and half ago.. i took the morning after pill on the 3rd day after intercourse... i came on my period a week after but it was dark and didnt last as long as my regular periods... i recently came on my period this month and it was still a dark period... ive been gettin really bad stomach pains aswell as backaches... is this still a side effect from the morning after pill or am i pregnant?