Period questions

Hey guys so I'm 17 and recently my periods have been coming 3 or 2 days late and I know I'm not pregnant because I haven't had sex in 3 months and I've been getting a period. But anyways I also usually get very bad cramps and backaches but this month I'm on my period now and it was 2 days late and I'm having no cramping or backaches is this normal this usually never happens  ? Also my period also lasted 3 or 4 days and this seems short to me it's my second day of my period and it looks like it could end tomorrow . So is all of this normal ?