Am I an enigma?

Hi all! My story…
I've always been overweight. In my early twenties, I worked hard to lose 50 lbs quickly, at about 70-80 lbs overweight. I had almost reached my goal, but wasn' t able to maintain the lifestyle, and slowly gained almost all of the weight back.  Fast forward to having my son at 28. I was the heaviest I'd ever been right after the delivery, and though I worked pretty hard for about a year after his birth to lose weight, I landed at my starting point pre-pregnancy, which was still around 50 lbs overweight. (I'm 5"6 and about 200 lbs).

The last few years I've worked with a dietitian, limited calories, and been regularly active. Currently I am training for a 10k and I run about 13 miles a week, cross train a little in between rest days, and eat balanced and proportioned. I don't eat any fast foods, not many refined sugars, and as of a few months ago, no artifical sweeteners either.

I have not lost any weight no matter what measures I take. Last year after many crying jags I visited my doctor with concerns about hypothyroidism because my mother and my grandmother on my father's side have it. Mom is currently being treated with synthetic hormones. Well, my bloodwork came back normal. M doctor did two tests...I believe T3 and the other more in depth test for antibodies? I know she told me that she was pretty certain I did not have hypothyroidism.  

It’s a year later--no loss. The only thing that seems to even cause a momentary dip in me is a low carb diet.  I try to keep my chin up, and change my workout up, but it's so frustrating. Is this "set point theory", or should I continue to examine the possibility of hypothyroidism? I don't want to go on a wild goose chase for a diagnosis or dwell on something that isn't true.

R.D. thinks cortisol or inflammation could be a cause? Another friend with a BA in nutrition and Eastern medicine wonders about food allergies.

If you made it through this--kudos. Any help or advice is appreciated! :)