Vitamin D Testing Frequency

[Juls]

I expected my Vit D to be very low ( Live in Scotland & Cancer) even though I had been taking a 1000 IU capsule on and off since August. Result of test = 72. . Unfortunately not tested when first diagnosed so can't compare. Magnesium is 77 so ok and Calcium just in at bottom of range (2.19/2.33)]. I am a little concerned about calcium being low but can't find any info on this. Any suggestions?
Will read up on resistant starch.