If you have had unprotected sex, then pregnancy is always a possibility. However...brown blood usually means old blood, so it could be left over blood from your last period. I say take a pregnancy test when your next period is due..
... you do not ovulate 2 weeks after your period - you ovulate approximately 2 weeks before your next period is due. So if your cycles are longer you will ovulate later on in the cycle.
The only way to know for sure if you are pregnant or not is wait until your period is due and then take a test if you are late. Many things can cause spotting and nausea. What you experienced could be ovulation spotting (since you typically ovulate 2 weeks after your period) but if you had sex then it is possible that could have gotten pregnant but it is usually too early for pregnancy symptoms (nausea/vomiting). Good luck!