What Are The Chances Of Pregnancy After Having Unprotected Sex?

I almost had sex with my boyfriend a week from yesterday but he was just in the outside and didnt go in. 2 days ago we had sex forreal and didnt use a condom he pulled out. Later that night my friend said that i could get pregnant from the precum, which i had no idea of. That made me extremely worried and stressed out. Yesterday i got plan be and took it about 24 hours after. Before i took it i kept getting a weird pinching/tugging feeling in my lower stomach which made me even more worried and my lower back started to ache. I took the plan b and it seems like the side effects are happening like cramps mood swings larger appetite, and it made my back ache even more. I know that there is no way that i could have pregnancy pain the day after i have sex but is it possible that i could have gotten pregnant from what happened last week for barely longer than a second? I have been going crazy with worry.