I went to the ER for abdominal pains on the left side and back. It felt like gas. I have gallstones and my amylase ia elevated by 19 points. The doctor says don't worry. Can it be a gb attack?

Pancreatitis. It sounds like you have gallstones that led to a bout of pancreatitis (we cleverly call this: gallstone pancreatitis). Both gallstones themselves and pancreatitis can give you abdominal pain; pancreatitis more commonly causes back pain. The treatment is gallbladder removal--so it doesn't happen again.
Possible Gallbladder. Typically pain from gallstones is in the right upper quadrant and follows eating a fatty meal. Gallstone pancreatitis can follow a gallbladder attack where you have more centralized pain which typically goes to the back. Amylase and lipase as well as liver function tests would typically be elevated. An ultrasound is typically performed to see if there are stones in the common bile duct.
Gallbladder disease. You may have had a gallbladder attack. Gallbladder disease or passing a gallstone can feel like stabbing pain into your back. The severity can be so intense, like a heart attack. Fatty foods make it worse. Some positions can make it better. See your regular doc, who will get you referred to surgeon. At the er you likely were not sick enough to meet criteria for inpatient care/urgent surgery.