You are most likely not pregnant, the change in your cycle is probably because of the plan b and it should return to normal next month.
Very unlikely that you're pregnant.
If u took a plan b it is highly unlikely that u are. The different shades of a menstrual doesn't really mean anything other than blood flow is different. If u want to be absolutely sure u can go to doctor.
Best to go to planned parenthood and have one of the nurses confirm for you.