Implantation bleeding or Period?

Hi,

My period was irregular for the past 2 years which only came up in 3 months once. Had my last period on the 23rd Dec. But today, on the 21st Jan, i had a bleeding. It was flowing non stop in red color.  Is it an implantation bleeding or my period? And i do not have any symptoms of pregnancy after intercourse about 2 weeks ago.

Thanks