Am i prego????????????

Ok so the last time i had was on December 17. I kinda think i might be prego but i dont know what to think because ino how everyone says how you cant tell that soon but my lower back has been killing me today i got my "periode" 3 days ago but now it seems to have stoped and it always lasts a full week. I am also having cramps in my stomach too. I usually just cramp the first and second day i have my periode but it is still bothering me. I have also been falling asleep very early in the last 4 days than i always do and i just feel more exhausted everyday. I also didnt have n apetite at dinner tonight and we had made my favorite foods. What do you guys think? Plzzz I need some help!!