If you were my patient, I would want to reassure you a bit. It is completely normal and expected for the hemoglobin to drop a bit as pregnancy progresses. Taking Iron is definitely a good idea, and you should follow your doctor's instructions on that. Fatigue is also very common, and often does NOT respond to iron. The best thing to do if you are tired, is to rest as much as possible--I know that often it is NOT possible to get enough rest. Drink lots of fluids (fluids with vitamin C will help you absorb your iron) and don't feel guilty about naps!
It will end!