implantation bleeding?

So I started bleeding on Sunday morning when I woke up (it's now Tuesday morning)   - my period is only supposed to start next week though. I have period like cramps, feeling dizzy when I stand, feeling tired and moody. I have taken a home pregnancy test and it came back negative. Could I be experiencing implantation bleeding or could it just be my period arriving early? My hubby and I have been trying for almost a year now and we were active during my peak ovulation