Eh, this is quite common in later pregnancy actually, your digestion really slows down and becomes more sensitive, plus the baby is taking up so much space lah! A few of us mums had the same issue in our 3rd trimester, some foods that were fine before suddenly jadi culprit. Since you're already 31 weeks and this is affecting your sleep, best to mention it to your doctor or midwife just to be safe, okay? Could be something simple like how you're digesting the iron or just pregnancy things, but they can advise you better on whether you need to adjust your diet or your iberet dose.