Aww sayang, 31 weeks and still throwing up macam ni memang exhausting! A few of my mum friends experienced the same thing in their third trimester, sometimes it's the baby pressing on your stomach, sometimes gastric flare-up, sometimes infection especially kalau ada cirit birit skali. Since it's been 3 days and you're losing fluids, better get checked at the clinic today je to make sure everything's okay and baby's fine, especially with both symptoms happening together. Minum plenty of water in small sips and rest as much as you can, take care of yourself, mama!