Total Eclipse
I used to take those ensures daily. They help with malnutrition to an extent but they aren't going to cure a major deficiency (creating your own protein drinks would be much healthier. It's good that your drinking those at the very least though).
Iron, B12, Folic Acid, D3, Thyroids, sodium, Magnesium, Testosterone levels, blood count/ platelets are all things a doctor would run a quick check on.
It's getting hotter outside and you do have a heart condition. That itself can make people lethargic and tired. I get very faint like in the summer >_<