Hi OP
I had exactly the same aches and pains as you describe.
I was also tested for Vit d deficiency by a consultant at the local hospital who I was seeing about a thyroid issue.
The GP was surprised that i had been tested for vit d but My Vit D levels were also the lowest the GP had seen. Even lower than the elderly folk who he looks after. 
He booked me in for a booster jab, and I swear the next day I felt like a new person! It was truly truly amazing. He also put me onto 2000iu per day.
I was on these for 6 months after which he couldn't prescribe them anymore. He told me that I didn't need them anymore. The consultant at the hospital was surprised that the p had prescribed them as the borough that the hospital were part of didn't. His advice to me after the gp stopped providing them was to buy the cheapest D3 Cholecalciferol tablets I could find and take them daily forever.
From what I gleaned from the consultant, Vit D testing is expensive and when I had my booster jab, the nurse said the supplies were really low.
I don't think there's any harm in supplementing your diet with Vit D, and from what I've read, it's safe to take much higher doses than you might think.
If there is a good health food shop near you, you will be able to get some advice on this. I found some of this stuff natures Answer for less than on amazon, and it lasts for ages.
The thing to remember is that you don't need it on the days that you get good exposure to the sun. Apparently 20 minutes of nude sunbathing at midday in direct sunlight is good for getting what you need daily. For most peeps though that's not gonna happen, so supplementing is the only way as it's not really found in many foods naturally.
In some parts of Europe the governments enrich more foods than we do in the uk as there is evidence about the benefits of vitamin d/problems caused by deficiencies in it. I also give it to my children in drop form during the colder dark grey months, so pretty much the whole of last year.
If you can get hold of some, you could try it for a few weeks and see if it helps. If it does, then I don't think there's any point in going to the gp for this, unless you can see a different one in the practice.
Just out of interest, when you were deficient during pregnancy, how much did the GP tell you to take?
Sorry for the long post but hope it's helpful. I'm nt medically trained but am still amazed by how much difference it made to me in such a short space of time, esp after enduring all those achey niggles for a few years.
Take care