Can implantation bleeding last for 4 days?

Kathy

I've been having dark brown bleeding since 4pm on Sunday that I've only had to wear a thin panty liner and doesn't even fill it. Finally stopped today but has me so confused because my periods are always really heavy with bright red blood and last for 7 days with the last 2 days being light bleeding. Do you think it was implantation bleeding or just my period being abnormal for some other reason? If it was ib when should I test?