What can I take for extreme and daily heartburn? I'm currently pregnant with twins, but my stomach seems to be hurting all the time.

Heartburn. If tums, mylantan, and maalox don't help try tagamet or Zantac (ranitidine) 2-3 times a day. If you still don't get relief you can try a proton pump inhibitor. The only one you should avoid is Omeprazole (prilosec) because it is contraindicated in pregnancy. Lansoprazol would be a good choice. Remember to take it 20-30 minutes before the first meal of the day.
Heart Burn. Heartburn associated with pregnancy can usually be treated with a proton pump inhibitor or ppi. All ppis are likely safe for breastfeeding. You can also take h2 receptor blockers, which are over the counter. However, being pregnant you should talk to your doctor about your symptoms and what is best for you!