I experienced hypoxia at birth and now have autoimmune diseases (celiac, benign goiter, pcos). are these related to my birth?

Unlikely: I am not aware of any connection between hypoxia and autoimmunity.

Maybe: Your story makes me ask the following question- why were you hypoxic at birth? Did your mother have any problems that you may have inherited to a certain degree. I do believe that your autoimmune problems are interrelated - resulting from hormonal, immune and nervous system imbalances. For example - gluten allergy causes inflammation which can affect thyroid (goiter) & increase Insulin (pcos).