I need advice.. and help

So im 16 and im in a happy relationship with my boyfriend. We have been dating for about 1 year and about to make 7 months. Lately,since i went to vacation at puerto rico, i felt nauseated and had stomach ache. At first i thought it was because of the curves of the street and going from up and down the mountain by car. I had my period for 4 days instead of 7 days and i had the cramps as usual but... for 4 days. I felt weird about it but i brushed it off. My mom just told me because it was because of i was in the water too much so it just went away. I still feel the same way however and till this day i felt the same symptoms like nauseated and stomach ache. I did have my period for about 5 days two days before i posted this. My boyfriend and i are scared about this because the day before i went to puerto rico, we had sex without a condom. He believes that i am pregnant due to the fact i have symptoms of pregnancy. We havent taken any test to see if i am and I havent told no one and i dont know what to do. What should i do? (june 10 i took plan B; i took it two days after we had sex without a condom)