What Causes Reduced Appetite, Bloating And Pain In Stomach?

Hello this is regarding my diet. For the past couple of weeks, I have lost my appetite and it s worrying my mum. I only end up eating one meal a day (portion is small - like breakfast). I am usually constipated too, however after losing my appetite my bowel movements are regular (everyday) but when I eat 2 meals a day I feel very bloated, full and my stomach aches. Do you know what s wrong with me?