Could Abdominal Cramps And Nausea Be The Symptoms Of Pregnancy?

Hi, I was wondering how soon you can start showing signs of pregnancy. My friends are concerned that I could possibly be pregnant, however I believe it could just be food poisoning. 10 days ago my boyfriend and I had sex for the first time, we used a condom and were safe, but I m not on birth control. 2 days ago I started feeling sharp pains and cramping in my stomach a few hours after going out to eat. I have been nauseous and I ve thrown up once. I ve also had diarrhea. The mere thought of food makes me sick and I have acid reflux. I m suppose to start my period in 6 days. I have a period tracking app on my phone and it says I was fertile the day we had sex. Could I possibly be showing signs of pregnancy or am I correct about it just being food poisoning??