My 21 y/o son gets chest pains when lifting heavy things at work and sometimes just while sitting.

Hello Friend,
How you're feeling better. Please take this as just a suggestion because without doing a physical or getting bloodwork this is a strong educated guess. Normally with the flu one of the things to be aware of is hydration. You could be undernourished and dehydrated if you experienced any diarrhea or vomiting with the flu.
the strong recommendation would be to hydrate with water and take some trace minerals to get your body back to normal working order. If the blurry vision or heavy headache or chest pains still persists, go to a physician. As sometimes a heavy headache could be a sign of meningitis, a rather serious condition. And of course chest pains, who like those?
As a side note, all of the conditions you list ...
headache, vision, chest pain at their core is sign of significant dehydration.

See a physician

Pleuritis. Also known as pleurisy, this condition is an inflammation or irritation of the lining of the lungs and chest. You likely feel a sharp pain when you breathe, cough, or sneeze. The most common causes of pleuritic chest pain are bacterial or viral infections, pulmonary embolism, and pneumothorax.11 Sep 2016

What Causes Chest Pain? Types of Chest Pain & Causes of Each

have chest pains in the right side of my chest Google Search

You should discontinue this over the counter vitamin regimen until all symptoms subside before considering restarting with a lesser dosage. Vitamins for people of all ages can sometimes exceed 100% for a given day's recommended total. When you combine this with the amount taken in through normal diet, for instance Calcium gained by drinking milk plus Calcium in the vitamin, you can risk an overdose on the vitamin. Overdose can occur with anything and this will pose certain dangers to children as they grow. While it is admirable to desire to provide children with all the vitamins and nutrients they require to grow, one must be careful not to over-do it, as the saying goes with too much of a good thing.

Could be a heart problem. Check with your doctor and don't wait. Could be serious or some other problem that need professional attention.
Bud

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