What Causes Light Periods, Tiredness And Sore Breasts ?

Hi I'm always regular with my period standard 28 day cycle and have a really heavy period this month It started when it should but is very very light was bright bred no clots and for the following 2 days very light almost pinkish. I'm tired with sore boobs. Is it possible I'm pregnant test show negative with my son I didn't know I was Pregnant results showed negative for a week after my period was due test shows negative could it have been implantation we are ttc