Havnt had period for 2 months then i had protected sex the next day i started very light spotting and it continued for about a week what could this be caused from is it implantation or just period?

Likely a period, but: A urine pregnancy test, done correctly, gives a reliable result 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, and a test is not needed.