i have question.

hi, i have question about that happen to me. I have no period. so do you know i have cramps before i have period? if i have no period then could i have pregurnt? Must i have go to doctor and i have to birth control then i have to get pill? i am not sure. i think soon i will get a period tomorrow or next week. but i have no period for 4 weeks then i will have period as soon? ?