Help pls

To make a long story I got my last period a couple of days earlier that it was supposed to come, today the app says I’m supposed to get my period but it’s only day 26 instead my period usually comes every 27 days. But today I have not gotten my period I have not had sex or penetration. I’m concerned cause I’m experiencing cramps on my right side and I was feeling sick this morning also my boobs are not really sore. I’m really confused and I don’t know if I should be worried or I’m just stressing myself out even more.... pls let me know