I have raynaud's, chilblains and dermographism. could they be related...possibly hypothyroidism?

YES!!: They are all Auto-immune disorders. Often they are seen in the same person.

Possibly: Raynaud's disease and chillblains are often considered autoimmune illnesses. Hypothyroidism is also typically an autoimmune illness. Dermatographism is not typically considered due to an autoimmune illness, but it is seen in people with hashimoto thyroiditis, which causes hypothyroidism. So there may be a connection between all of these.

Not so much: Raynauds and Chilblain's often are mistaken for each other but are different in the pathology that causes each other, it isn't that uncommon for people to suffer from both though. Dermatographism is quite different and not as common to be found in conjunction with the previously mentioned issues. Hypothyroidism seems to be more strongly associated with Raynaud's>dermatographism>chilblains.