Pain In Stomach After Eating. Had Diarrhoea, Feel Dizzy, Fatigue. Not Pregnant

For the past few days I ve felt sick to my stomach. I also feel sharp and dull pains in my stomach (mostly the mid and upper areas) especially after eating. I ve had diarrhea, but I can t tell if there s blood in it (I m on my period). I feel marked dizziness when I stand up. I feel unbalanced. Throughout the day, even though I ve slept a good amount at night, I have a sudden wall of fatigue hit and I feel like I can t even keep awake. More rarely my heart feels like it s racing and I feel really hot. I m 20, I smoke, I exercise regularly, I eat healthily, and I m not pregnant. I don t have a history of health problems.