You have reason to be concerned.
Why? Because depending on your fertility cycle, you can still become pregnant, as sperm can live in the vagina for as long as a week. So, if you ovulate early this month or regularly? They can be there waiting for the new egg following your period.
As well, you have STDs and STIs to concern yourself with. Consdiering the highest rate of STI transmission is in those under 24, and mainly because that age group doesn't worry about it and tends not to have protected sex, there's plenty of cause for concern there.
If it has been less then 72-100 hours since this happened, you can obtain emergency contraception. And in the next month, you and yours should be sure to have your yearly STD and STI screens, if you don't so that already.
And you most certainly should sit down and discuss WHY you need to be using condoms, and make a hard rule to do so henceforth, as well as a backup contraception method should you choose.
Editor and Founder, Scarleteen
My epitaph should read: "She worked herself into this ground."
-- Kay Bailey Hutchinson