I've been feeling naseus, extremely tired & crampy for 4 days & I've been having unprotected sex with my boyfriend could I be pregnant?

Possible. If you have unprotected sex any one of the 5 days leading to your ovulation you can become pregnant. You did not give your ovulation and sexual history. I can not predict . All i can say take a pregnancy test one day after if you missed your period.
Consider testing. Having unprotected sex without contraception definitely puts you at high risk of becoming pregnant. Consider pregnancy testing.