You are very young to be having these issues. I don't recommend DHEA for women. I would try some alternative therapies. Give acupuncture or a homeopath a try if you can afford it. Some insurances will pay for acupuncture.
I take DHEA on my doctor's orders. I take 25mg. However I have no adrenals - but since you have low DHEA, perhaps you could use it as well.
Do know that DHEA converts into testosterone OR estrogen and it is not your choice, and if you take too much DHEA, you will know it, you will get acne and your skin will get greasy.
Some of my friends take less, some take more - I sometimes take less as I get acne.
You can try a little of a reputable brand and see - but the tests it will impact are not so much thyroid but are the androgens. It is generally felt that it helps one sleep better, have a better sense of well being at least in those without adrenals.
I also use accupunture - and I love it - but it does not raise my DHEA-S levels.
DHEA deficiency is a common problem leading to imbalances of estrogen, progesterone and testosterone. Supplementation of the DHEA can often times fix the imbalances (and therefore symptoms) of these other hormones.
DHEA is best formulated but a company called Ortho Molecular. The sell only medical grade supplements that have to be provided by a licensed practitioner.
I take other brands as well as I have taken DHEA compounded for me by my doctor. As long as you take a reputable brand, you should be fine. I let my doctor know my brand.