Nauseous and Lightheaded during workouts

For some reason despite eating an hour before, right before, or after, anytime I workout at the gym / lift weights I get lightheaded and nauseous.

I can play sports, walk lots, etc and I don’t really ever feel this way. What could it be? Is this common? I have been trying to better my health and physically get stronger but for some reason I’m so sick at the gym all the time.

I can typically walk on the treadmill and be fine but then afterwards when I get off I immediately feel sick.