Should I buy Plan B?

So I lost my virginity Friday night, we used a condom (and checked for tears/holes afterward- there were none) but eve says it was my fertile window. He did cum inside of me but obviously it was into the condom.  I'm not on birth control and I'm very sensitive to hormonal treatments so I'm not sure if I should get Plan B or not. Is it necessary? Or should I just stop worrying?