I've been feeling very weak lately, could it be because my vitamin d is really low?

Doubt it.: Would be unusual to be Vit D deficient in Boca Raton at age 19. Secondly, VIt D deficiency does not usually lead to fatigue or weakness.

Fatigue/ weakness: Fatigue or weakness are general symptoms that may be related to several broad conditions. Blood/ circulation problems like anemia ( decrease red blood cells). Endocrine (low thyroid). Vitamin D or B12 deficiencies. Metabolic causes like low sugar. Respiratory like sleep apnea or neurologic causes. Viral causes like mono. One should have a thorough evaluation with his or her health care provider.