Have you assessed your calcidiol [25(OH)D] levels?

I have no direct answer to your question, but I would like to point out that
in theory it is possible that their could be a dysregulation of
1,25-dihydroxyvitamin D synthesis although it is very rare.

http://bmj.bmjjournals.com/cgi/eletters/326/7387/469#30163

I think that first you should get your 25(OH)D level tested to see, if
you indeed have a deficiency. Unfortunately the results of 25(OH)D
test can vary by upto 30% between different commercial laboratories.
So you cannot blindly rely on the test result, but it should give some
indication. Vitamin D3 has been given as intramuscular injections at
doses 100 000 IU upto 3-4 times a year, or even 600 000 IU once a
year. With megadoses intramuscular injections are preferrable to oral
route, because oral dosing causes higher peak in 25(OH)D level.
Your doctor can prescribe the dose, and a nurse or actually anyone,
who knows how to give an intramuscular injection, can administer it.
Some people even do it by themselves, but that requires a little bit
of knowledge and practice, which one can however get fairly quickly by
finding a medical professional to teach how to do it.

Here some related Medline references:

Alyaarubi S, Rodd C.
Treatment of malabsorption vitamin D deficiency myopathy with
intramuscular vitamin D.
J Pediatr Endocrinol Metab. 2005 Jul;18(7):719-22.
PMID: 16128249 [PubMed - indexed for MEDLINE]
<http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=Abstra
ctPlus&list_uids=16128249>

Diamond TH, Ho KW, Rohl PG, Meerkin M.
Annual intramuscular injection of a megadose of cholecalciferol for
treatment of vitamin D deficiency: efficacy and safety data.
Med J Aust. 2005 Jul 4;183(1):10-2.
PMID: 15992330 [PubMed - indexed for MEDLINE]
<http://www.mja.com.au/public/issues/183_01_040705/dia10054_fm.html>

   "Conclusions:

   Once-yearly intramuscular cholecalciferol injection (600 000 IU)
   is effective therapy for vitamin D deficiency. While this therapy
   appears to be safe, the potential for developing hypercalciuria
   needs to be examined in a large randomised controlled trial."

Vieth R.
Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and
safety.
Am J Clin Nutr. 1999 May;69(5):842-56. Review.
PMID: 10232622 [PubMed - indexed for MEDLINE]
<http://www.ajcn.org/cgi/content/full/69/5/842>

  "Depot injection or intermittent large oral dosing with vitamin D
   
   Another way to augment vitamin D nutrition has been to
   administer vitamin D as a single large dose, either orally or
   through injection. Because vitamin D has a half-life >1 or 2 mo,
   a large dose should suffice for the better part of a year. The
   approach is often called stoss therapy (from the German for to
   bump) and it is most common in Europe. One Finnish study, by
   Heikinheimo et al (80), concluded that annual injection of
   vitamin D2 in the autumn (3750–7500 µg, or 150000–300000 IU) can
   lower the probability of osteoporotic fractures by 25%. Note
   that before treatment, the mean 25(OH)D concentration in the
   untreated control subjects was only 16 nmol/L, and thus, much of
   the fracture prevention appears to have been attributable to
   raising 25(OH)D concentrations out of the osteomalacic range.
   The effects of single large doses of vitamin D are summarized in
   Table 6. Only a few studies monitored serum 25(OH)D
   concentrations during the days, weeks, or months after
   administration of large doses of vitamin D. Both Davie et al
   (28) and Weisman et al (87) showed that with oral dosing, there
   was a relatively rapid peak in serum 25(OH)D concentration, with
   concentrations falling progressively afterward. When doses were
   administered intramuscularly, there was a longer-lasting
   response in terms of serum 25(OH)D. However, in some cases it
   took 2 mo for the peak concentration to be achieved. In the
   study by Heikinheimo et al (80), serum 25(OH)D concentrations
   after injection remained higher than those of the control group
   for the entire year."

The above mentioned table 6:

TABLE 6. Effects of single large doses of vitamin D
AJCN -- Vieth 69 (5): 842 Table 6
<http://www.ajcn.org/cgi/content-nw/full/69/5/842/T6>