know any causes of Chronic Nausea?

I'm really really seeking any type of insight into unusual or rare causes of chronic nausea. I am a 27yo female and have had chronic moderate-severe nausea daily for going on 10 months with no known cause. I have ruled out pregnancy and GERD, and know that it is not from anxiety (I am a MH professional). It is seriously debilitating and I have seen many specialists that all have coincidentally found something but not the cause of the nausea. The other symptoms I have include headaches, palpitations/PVC's, chronic fatigue, occasional nightsweats, dizziness/chest discomfort when standing up, and just an overall sense of unwellness. In the midst of this search for answers I was diagnosed with Hashimoto's, but dont believe it's the cause for many of these symptoms as the lump in my throat feeling and fatigue have improved a little w/ Hashimotos treatment but most of the symptoms I mentioned previously have only continued to get worse. Does anyone know of any possible causes for the symptoms I have been struggling with, particularly the nausea? Or is anyone familiar with Hashimotos and has had a similar experience of having this intense persistent nausea for months?? I feel like my medial providers aren't thinking outside the box and aren't taking it as seriously as I am to consider potential causes. I feel very desperate as I can feel myself getting sicker. This will sound dramatic but since I have only continued to get sicker over the past 10 months its hard not to wonder if I have some type of serious illness thats just going untreated. Thanks in advance.