Yes blood test for Vitamin D is inexpensive make sure you get your Vitamin D2 and Vitamin D3 tested. I had a number of 9 now I keep it around 60 which is good for me. Normal Range should be around 50 must doctors will disagree with that number. My doc. is great she wants that number around 60 not 25 which is on the low side.
Tinned Tuna in oil, and cod liver oil capsules are a great source for vitamin D. Other good sources are Oysters, oily fish, fortified cereals,