I'm 26 and during my last physical the doc asked me if I wanted to be tested for Vit D and I said yes. For the 25 years prior, it must not have been a big deal in the healthcare industry, b/c they never asked me...He also told me to check with my insurance and make sure the test was covered by my insurance as part of the yearly physical/check-up. The results came back that I was severely Vit D deficient. He told me to start taking 5000 IU of Vit D daily for 3 months. Also, OP, you can get 5000 IU in one small ass pill (what I take)
[ame=http://www.amazon.com/gp/product/B004N8TTBQ/ref=oh_details_o03_s00_i00]Amazon.com: Vitamin D3 GOLD - 5000 IU (360 Softgels) Naturally Sourced Preservative-free Vitamin D: Health & Personal Care[/ame]
I feel soooooooooo much better now (8 mos later). I have more energy, feel stronger, and havent been sick since like the OP (I used to get sinus infections and head colds all the time).