My Husband Seems Tired And Listless Most Of The Day

My husband seems tired and listless most of the day and is sleeping a lot. He is 76 years old and had an aortic valve replacement and 3 bypasses 18 months ago which seems to be working just fine. He has a strange sensation in his stomach (no pain). His appetite is low. He had his blood checked recently and the only that they saw is that his hemoglobin is at 12. He seem to be grasping at straws as to what will make him feel better. He also had a hemocult done recently with no blood in his stool.