I'm in a lot of pain in my abdomen and my lower back?

Need more info.: If this only a simple Muscle pain or Menstrual Cramps; treat with Tylenol (acetaminophen) or Midol or Ibuprofen. If there are some other issue then accordingly.

Depends: Abdominal pain, even if severe can be due to a number of causes. It could be anything from simple constipation to something very serious. If constipated, take 2 TBS of milk of magnesia (magnesium hydroxide) with 2 large glasses of water. You should get relief in 4-6 hours. Otherwise go to an urgent care clinic ASAP and get evaluated and treated.