Period 5 days early while TTC

Hi ladies,

Been TTC for 6 months now. Have always had a very regular period. However last night I felt cramps and sure enough my period came 5 days before it’s expected date. This has never happened before. I was hoping it was implantation bleeding but I feel that the cramps are too strong and it’s a bit too heavy to be implantation bleeding.

Does anybody know why this may be? Or has anyone has a similar circumstance?

Thanks in advance x