A fever in third trimester can feel quite worrying, but from what I've heard most mums get through it fine with rest and fluids. That said, since you're in your third trimester it's really important to check in with your gynae or polyclinic just to be safe and make sure it's nothing that needs attention, especially if the fever is high or lasting more than a couple of days. They'll be able to monitor you and baby properly and put your mind at ease. In the meantime, try to rest as much as you can and stay hydrated lah.
Asmulina Binti Abu Bakar