Acne , Unintentional Weight Loss, Stomach Ulcer?

Since like 4 months ago ...i started having acne and stomach pains and i started losing alot of weight. The dr told me it was an ulcer and to take omeprazole and it will heal .But i just keep losing weight ...from 70 kilos im now on 64.....ive never been this thin. Im a 6 feet tall guy. What is happening? Im scared im really sick and i dont know it