can u get pregnant 1 day after period ended and then spot a week lAter

Get some OPKS. It will take a lot of guess work out. They are very cheap and easy to use. You’re likely having ovulation spotting or normal mid cycle spotting

Not impossible but highly unlikely

If you ovulate that soon, yes.

Most likely, no. Some women spot around the time they ovulate and that sounds like what could have happened.