What you’re talking about is anemia. There are many causes of anemia. There may be a kydney problem which requires a specific pharmacological treatment. The bone marrow may not be producing new red blood cells, or there might be a deficiency in hemopoetic cells in the marrow. There’s a million reasons for anemia, each with a different specific therapy.
Most of these require prescription:
Carbonyl Iron
Cyanocobalamin
Ferrous Fumarate
There’s one relatively new drug that produces a lot of RBCs very quickly. It requires a weekly injection at a cost of about a grand a pop. They use it on cancer patients mostly, leukemia and Sickle Cell anemia victims. Serious stuff. Epoetin beta-methoxy poly blah blah blah. You might find some down at the racetracks. They illegally shoot up race horses with it sometimes. Makes ‘em run super fast and forever. Blood becomes packed with RBCs. Almost unlimited O2 to the muscles. High risk of stroke, but what the hell, as long as they win.
Or you could just take the old lady down to see a doctor.