Had my period 3 weeks early after taking the plan b could I be pregnant

If you hve your period, you are not pregnant,
That is normal

Was the period lighter than normal ? At times you may have a short light period when first pregnant,

But as you surely read on the warnings of Plan B, it can and will have an effect on your cycle for a couple of months.

And as you read also, I am sure you know that plan B is not 100 percent effective you can still get pregnant if you take it, the sooner you take it after sex the higher the effective rates