Since you just ended your period and if you are fairly regular I would say it doesn't appear that it would be implantation bleeding. Now everyone is different and in reality a person can ovulate at any time. Usually implantation would occur about 7 days or so after conception. So with you only having been off your period a week and if you are regular each month it wouldn't point to that. (Unless this last period you had that ended on the 20th wasn't normal as the others are) Spotting can occur at any time for a variety of reasons. Some of those reasons are; stress, weight gain/loss, medication, illness, climate, cyst, or polyp of the cervix, hormonal balance, even infection and or std could cause the spotting.

That's why at this point you just need to keep track of days and how your flow is. Wait till next month and see what happens with your flow. If you feel as though you may be pregnant there is a HPT on the market called First Response, it states it can detect HCG (pregnancy hormone) up to 5 days before a period is even missed. Now how true it is, I don't know. But that is what they state.

Hope some of this helps Hun.