I still recommend pushing your doctor for more tests or for finding a new doctor who will run the necessary tests.
as for vitamins there is still massive debate over vitamins and supplements. this is good, no it's bad, no it's great, no blah blah blah... you will get five different opinions from every single person you ask (with some people contradicting themselves).
the best thing to do is to run a Spectracell (or similar test) or get blood tests of certain things (per the blood test sticky) and then try and fix those things that are not ideal - otherwise you could just end up overdosing your system on something and causing more problems.
that being said there are a few universal suggestions I keep hearing over and over again:
Vitamin D3 - at least 6,000iu (liquid or gel > powder)
A good overall multi-vitamin
Fish Oil Essential Fatty Acid (dosage recommendations varies)
200mg Vitamin E (Mixed Toco - not just your basic Vitamin E)
Niacin 100mg - 1000mg (depending on how much you can stand - IF you need any help at all with lowering LDL and raising HDL)
other vitamin/supplement options include:
IF you have low ferritin/hemocrit/hemoglobin then reduced or elemental iron 20-30mg + 2,000mg Vitamin C to assist with absorption can be helpful.
some people swear by CoQ10, Green Tea Extract, and Revertasol, but they had weird side effects with me.
If you have thyroid issues, then some recommend 12.5 mg Iodine and 100mcg Selenium.
Probiotics and Digestive enzymes can be helpful for some people as can Betaine HCL (it's amazing the number of people who take acid blockers who are actually getting acid reflux due to too little acid, instead of too much.)
A lot of men also take 25mg Zinc to help with hormone control. If you take more than 25mg, you should consider taking 2mg copper to help offset any copper loss due to extra zinc intake.