Period again?

Jamie

So my period ended on the 31st last month, I’m not supposed to start again until the 21st but today I noticed what was some light spotting. Didn’t think much of it but then it’s now turned into full on heavy bleeding, TMI warning but enough so that’s it’s gone through two layers of clothes and I’m having pretty bad cramps. Is it normal for me to be having another period like this essentially two weeks early?