Hv, I have gingivitis as well. It worsened through my vitamin c megadosing with Dr Lam.

I don't believe in megadosing of vitamin C.  There are too many potential problems including the formation of kidney stones and "teaching" the body to dump excess vitamin C, which can lead to "rebound scurvy".

I also do not like the Lipo C:

http://curezone.org/forums/fm.asp?i=1746946#i

I am currently taking 1000mg of amla and 1000 mg of Quantum. My gums continue to be severely swollen. I don't believe it to be from plaque as my dental hygene is perfect, although I haven't had my teeth cleaned for a while for fear of damage, because my gums are so sensitive.

You may want to try a different toothpaste.  Many of the commercial toothpastes actually damage the enamel and I think the sweeteners they use contribute to plaque formation.  I find when I use most commercial brands that the plaque forms faster than using herbal brands or just brushing without any toothpaste.  Look in to Auromere, which is a great herbal toothpaste.  And the herbs in the toothpaste help to kill the bacteria that contribute to plaque formation.

What other vitamin deficiencies could be causing this?

Some B vitamins or lack of the mineral silica.

I know that mercury toxicity can cause gingivitis. I only have one filling, but that tooth hurts especially bad and based on xrays it is free of cavities. My hair analysis showed extremely high levels of mercury.

I don't believe in hair analysis either.  The accuracy leaves a lot to be desired.

Otherwise, I seem to have a systemic chronic Candida issue and I've read that oral Candida can cause gingivitis as well.

Candida overgrowth in the mouth would appear as thrush, which is pretty easy to see.

I'm scheduled to have my teeth cleaned this Wednesday, but I feel like the wrong move could puncture my gums, they are so swollen.

Another trick is to get some pau d' arco powder and put a pinch on your toothpaste when you go to brush.  The pau d' arco kills bacteria and fungus and contains 5 anti-inflammatories.

I'm currently oil pulling with coconut oil and oil of oregano. Hydrogen peroxide made shooting pains in my teeth so I'm no longer doing that.

Your thoughts? Suggestion? Thank you!

One last one, stay away from the peroxide.  Commercial 3% peroxide solutions contain acid stabilizers that can damage tooth enamel, especially if used frequently.  The peroxide can also kill off the beneficial bacteria in the mouth leading to other issues.