Are there any Physical Illnesses, like diseases, that can cause Schizophrenia, Psychosis, Depression or mimic symptoms of those mental illlnesses?

Ive had strong feelings that there was a physical problem that could have caused all this. Ive been to doctors a few times and had tests done about other symptoms that I thought I had and it all came back good. If there is nothing wrong with me physically than I guess all this has to be in my head or something, which I dont really believe.

Also, can mental disorders cause physical symptoms?

Ive had physical symptoms like poor circulation, leg cramps and other cramps, fatigue, constipation, I cant concentrate, trouble breathing, heart palpitations. I realize that some of it might be from anxiety, but I dont know.