my period is 4 days late and i'm scared

i have a pretty long cycle since i lost my virginity, around 30 days. and now i'm 4 days late. the last time i had sex was 3 weeks ago, i didn't use protection and he didn't ejaculate inside me. i've been having bad cramps, back pain and headache for a week (normal pms symptoms for me). i've only been sexually active for 3 months so i don't know much about it. i'm really scared if i'm gonna get pregnant because we probably gobba break up anytime soon because he's been acting so cold and distant for 2 weeks. i'm so stressed guys please help, can i be pregnant? and for anyone who have been pregnant when fo you start to feel any change on your body and when do you first notice the symptoms?