Unexplained, very noticeable bloating. fluctuates, sometimes painful, look pregnant, test was neg. have mirena (levonorgestrel) 6yr, no history of gas(etc) issues...??

Fermentation: Most likely your symptoms are combination of nature of food consumed (gas producing foods), nature of bacterial colony in the intestine (like bacterial overgrowth) and food staying in the intestine longer. You can trying avowing culprit food and treating your constipation (if any), otherwise you should see a Gastroenterologist. Thanks