I'm a psych major (along with major biology and minor soc). There are numerous fields of study for psychology, anything from developmental to abnormal to therapeutic to forensic to neuro/biological and plenty others. My focus in psychology is purely in neuroscience/neuropsychology, that is, I still study developmental, abnormal and so forth through biological perspective, although there is always recognition of environmental factors.

It is not contradictory to be a psych major if you have a mental illness. You'll learn of mental illnesses, some of which you have, many of which you don't, and your first-hand experience will allow you to understand the content from more angles than students who don't have a mental illness. Chances are though, there will be students in the class who also have a mental illness, maybe even the same as you have. If I were in your shoes and T laughed, I would take it as encouragement to continue the psych major to show T you're stronger than even he/she thought and T knows you quite well.

In short, it's only an uphill battle if that is how you view it.