how long off the pill,
if your cycles were normal past six months then your most likely time to be impregnated would be a full week prior to your PROTECTED SEX which makes the odds very very low of pg,
ALTHOUGH the egg can take 6 days and sperm can live 3 days but not that likely
the pg test if from a grocery store etc may not be much good for three weeks but on the 28th most likely it is accurate.
now as to the rest that seems like a reason to go to the DOCTOR
hope this was not confusing