We had intercourse, now i have a really bad cramps in my stomach and my lower abdomen

Hi my name is Vanessa I'm 14 years old and I'm getting a little worried because I'm not sure if I'm pregnant or if it's something else but a week or so ago me and my boyfriend had sex it didn't last very long but now I'm having really bad stomach cramps in my lower abdomen and my uterus is swollen my back has been hurting I've been more tired lately and every morning I wake up with a severe stomachache and I'm nausus but instead of throwing up I have diarrhea also I was constipated at first I go through the whole day with cramps in my lower abdomen and when I eat I get very nausus please help I'm scared