what's the verdict? Pregnant or no?
There is a chance of pregnancy every time you have unprotected sex. Sad but true. It is less likely on some days such as when on your period. You got your period June 16h. Well, you were no more likely to get pregnant June 18 than June 16. Maybe you didn't get your period on June 16th but some time before that. But regardless, you probably hadn't hit your true more fertile time. That begins on day 9 of your cycle (day one of your period is cycle day 1).
But since all unprotected sex risks pregnancy, you can take a pregnancy test. You can get an accurate test at 2.5 weeks after the sex you are worried about. FYI, nausea does not typically start in pregnancy until week 6 to 7 of pregnancy. It takes that long for the hormones to build up to cause the symptom. Being tired is more common early on and maybe some back cramps. But only a test really should be used to determine and you should be able to take a test now to know. Come back and tell us.