Single digit vitamin D levels reflect a very depleted state. It is fat soluble, but difficult to take too much if you follow some simple guidelines. You will feel much better when you get your D level up to normal. Vit D does much more than build bones. It makes many systems work better and more efficiently; the muscles, nervous system, immune system. Normal levels are needed t fight cancer.
Prescription pills are available. Each contains 50,000 units. If it is convenient to get a prescription, I advise 50,000 units two times a week for eight weeks, then you can change to over the counter and take 2000 units daily to maintain your level. After 10 week from the start ov your replacement recheck the D level. On the internet you will find many different opinions about a normal D level. Low to mid 30's is fine. You may have to adjust your daily dose to maintain that level, but you can do it with over the counter D, taking somewhere between 2000-5000daily. Sun exposure is how we normally acquire vitamin D, but low levels are just as common in the sunny states, as in the snowy ones. That is because as we age we not only spend less time in the sun, but the skin becomes less effective in converting sun to vitamin. I'm sure you'll feel a lot better.