Plan B?! Question

Hey everyone! Has anyone ever had any horrible side effects to plan b? Im planning to take it since i was really bad with my BC and had intercourse with someone without protection. Is there any change of pregnancy? I missed a couple days but took that pill the next day etc. Any advice? I don't want a kid right now so plan b is a choice but im not sure if i should take it or if its worth all that money :(