I'm 16. I had sex about a month ago with my boyfriend(unprotected) 3-4 weeks ago and he didn't finish in me at all, but now I'm a week late for my period. My boobs hurt I'm cramping a bit but no period. I'm not getting any morning sickness or anything. Should I be worried or just see what happens?
Yes, you should be worried. From the approximate dates you posted you likely had sex just about near when you'd be most fertile, around ovulation.
Take a home pregnancy test. Use your first morning urine, your wake up pee, for the best accuracy. Use a name brand test, not a cheap one. Testing early, false negatives are common. False positives are VERY rare.
If it is negative, wait another week or so then retest. At that point if it is negative, and no period, you should see your doctor to find out why you've missed your period.
It is important to find out if you are pregnant early. You'd need proper pre-natal care.
Good luck. Please let us know the results. Post back at any point if you have any more questions.