help me, please

my boyfriend and i had unprotected sex 8 days ago, but he pulled out before he ejaculated... my last period was the first through the fifth and this app is telling me that i should start again tomorrow. the past two days i have felt like i could be constipated and couldn't really poop. i told two of my coworkers that have been pregnant before and they were teasing me about a possible pregnancy. is it possible? one of them told me that she was going to bring me a test to work, so i can see... i am kinda scared.