Heeelp, Could I get pregnant?

I had unprotected sex on the 26th of January. 2 weeks later I started throwing up and feeling nauseous, I wasn't sick or anything, just throwing up and not being able to keep anything down. That went on for about 3 weeks. I was supposed to get my period on the 15th of February but I got a light period a week later on the 21st of February that lasted about 3 days. Later I had unprotected sex on the 3rd of March and then had unprotected sex again on the 12th of March. I got what I'm assuming is my period 6 days early. I was supposed to get it on the 20th of March but got it on the 15th of March. I started feeling a little nauseous again today. Being pregnant never crossed my mind in February until my sister mentioned that it could be a possibility. I took 3 pregnancy tests during the 3 weeks that I was feeling sick to my stomach all coming out negative. Pregnancy only crossed my mind this time around because my boyfriend mentioned it. I'm always on time and accurate with my periods. They're always exactly 28 days apart and always last 4 days. The only symptoms I get when on my period are cramps and nothing else. Can someone give me a little inside? I'm only asking out of curiosity and wanting an outsiders opinion