I had unprotected sex tuesday 10/6 it been atleast 4/5 days now this linea nigra appear on my stomach & i been feeling bloated & lower back ache but my partner pulled out so should i be worry about being pregnant plus my period ended at the of octob?

Hard to guess: If worried, can do a pregnancy test. A urine pregnancy test gives a reliable result by 3 weeks after sex (3 weeks after when conception might have occurred), or 1 week after missing a period. If done sooner, a positive result is likely real, but a negative result may be due to testing too soon, and thus lead to a repeat test. If a woman gets her normal regular period, then she is not pregnant.