Autoimmune Disease? Tooth Decay / Lots Of Cavities

I'm a 24 year old female. I've been trying to figure out what is wrong with me for years. Two doctors, and two dentists, suggested that I may have an autoimmune disease, but I've had no diagnosis. I am wondering what autoimmune disease in particular this might be closest to. I've had these symptoms for a long time:

- Mild arthritis in right hand (since 17 years old) - maybe once a year, my fingers unexpectedly become swollen and arthritic, and then it goes away after a few weeks. It was most severe a few years ago, when my fingers became very swollen, hot, itchy and red, but it eventually calmed down and has not since returned with the same severity. My fingers in this hand are tilted towards the side, the joints have bended a little a bit sideways. Both of my hands and fingers are always very cold.

- Chronic fatigue

- A skin rash, cluster of small red bumps, that comes and goes on the side of legs. Also get random isolated red bumps throughout the body.

- Underweight and can't easily gain, though this might be genetic. I've always been underweight.

- Hair loss (began at age 18)

- Brain fog

- Vision getting blurrier / sensitive to light

- Eyes sore and red especially in the morning

- Poor looking skin

- Chronic sinusitis for the past 3 years. No cure or known cause (allergies were ruled out) - the sinusitis and red eyes clear up on steroids and antibiotics, but come back afterwards. So possibly a bacterial cause.

- Low blood pressure, low body temperature (96.5 - 97.5 on average)

- Tooth decay. I've had a lot of tooth cavities since I was a teen. I often wonder if tooth decay is the underlying cause of all of my problems. I've had many fillings and a root canal, but continue to have seemingly never ending problems with my teeth. My oral hygiene habits are extremely thorough though, and I try my best to prevent the cavities. I do everything I can to keep my mouth and teeth clean; electric toothbrush, brushing, flossing, special mouthwash, special toothpastes, etc.

I eat a relatively healthy diet and take vitamins and nutritional supplements. I've been experimenting to find the best diet to cope with this..whatever it is. I notice my health and energy levels are very dependent on how well I eat. If I eat junk food, or even the standard American diet, I feel very ill, exhausted and can't function. I can't have "treats" like a cookie or brownie, doing so could make me feel miserable for the next 24 hours. I keep myself semi-functioning by eating as simple and clean of a diet as possible, and consuming a lot of fruit and vegetables every day, along with tea and coffee.

My top two suspicions are that this is all a manifestation of tooth bacteria, or Celiac disease. Or maybe both. Most dentists don't believe that tooth bacteria would cause such an elaborate array of health problems, but I think it might be possible. I've heard of meningitis and heart disease caused by tooth decay. All of my symptoms started after I started to get severe tooth cavities, it was after having a root canal when I began to have severe hair falling out, and from then on my health went downhill. I had a blood test for celiac by a gastrointestinal doctor and they told me the results were negative. I never had an intestinal biopsy.