I feel very weak, tired and nauseous after eating. could it berelated to gallbladder?

Possibly: Nausea after eating, especially fried or fatty foods, may be due to gall bladder disease. An ultrasound of the gall bladder should confirm or rule out gb disease.

Nausea: Could be, could be other causes still like peptic ulcer disease, pancreatitis. You should see a doctor.

Gerd/ gallbladder: This can be gastritis, gerd, or other GI issues recommend seeing your pcp or GI doctor to begin work up and get you proper medications and or diagnostic tests.