I found this when I googled for side effects. I don't take any supplements, they may help what you need but they can also do a lot of damage in other places. They are drugs, unregulated and no guarantee that there is any V D in the bottle.
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Vitamin D Side Effects & Safety

Vitamin D is LIKELY SAFE when taken by mouth or given as a shot into the muscle in recommended amounts. Most people do not commonly experience side effects with vitamin D, unless too much is taken. Some side effects of taking too much vitamin D include weakness, fatigue, sleepiness, headache, loss of appetite, dry mouth, metallic taste, nausea, vomiting, and others.

Taking vitamin D for long periods of time in doses higher than 4000 units daily is POSSIBLY UNSAFE and may cause excessively high levels of calcium in the blood. However, much higher doses are often needed for the short-term treatment of vitamin D deficiency. This type of treatment should be done under the supervision of a healthcare provider.

Special Precautions & Warnings:
Pregnancy and breast-feeding: Vitamin D is LIKELY SAFEduring pregnancy and breast-feeding when used in daily amounts below 4000 units. Do not use higher doses. Vitamin D is POSSIBLY UNSAFE when used in higher amounts during pregnancy or while breast-feeding. Using higher doses might cause serious harm to the infant.

Kidney disease: Vitamin D may increase calcium levels and increase the risk of âÂÂhardening of the arteriesâ in people with serious kidney disease. This must be balanced with the need to prevent renal osteodystrophy, a bone disease that occurs when the kidneys fail to maintain the proper levels of calcium and phosphorus in the blood. Calcium levels should be monitored carefully in people with kidney disease.

High levels of calcium in the blood: Taking vitamin D could make this condition worse.

âÂÂHardening of the arteriesâ (atherosclerosis): Taking vitamin D could make this condition worse, especially in people with kidney disease.

Sarcoidosis: Vitamin D may increase calcium levels in people with sarcoidosis. This could lead to kidney stones and other problems. Use vitamin D cautiously.

Histoplasmosis: Vitamin D may increase calcium levels in people with histoplasmosis. This could lead to kidney stones and other problems. Use vitamin D cautiously.

Over-active parathyroid gland (hyperparathyroidism): Vitamin D may increase calcium levels in people with hyperparathyroidism. Use vitamin D cautiously.

Lymphoma: Vitamin D may increase calcium levels in people with lymphoma. This could lead to kidney stones and other problems. Use vitamin D cautiously.

Tuberculosis: Vitamin D might increase calcium levels in people with tuberculosis. This might result in complications such as kidney stone

Vitamin D is an essential vitamin and if you have (cholesterol and sun) your body will make it. As far as reading most of these scar tactics that they use to get you not to supplement phrases like could, might, may, possibly are used to make you think they are fact. Anything to excess is dangerous even pure oxygen would kill. Supplements are still safer than petroleum based drugs.

Love, what makes you think that vit. D is the culprit?

Are you taking vitamin D3 or a prescription vitamin D? If it's a prescription, google the name of the med with the term 'side effects, muscle pain' and see what you find.