Psychologist or Psychiatrist for me?

Hello I am not sure what my actual issue is, but its been over 7-8 years and past two years this has increased immensely. Medically severe throbbing at back of head and it's not migraine, severe aches, high BP with other issues but these being constant. From non medical side, constant fights between my mind and health, I feel like two people in my head; very contrasting mood swings. I feel super agitated, annoyed and low at times. Suicidal thoughts are very infrequent but yes they do exist in relation to harming self. I am struggling to live well and not sure how badly I am depressed or has affected my mental health. Personally, yes I have suffered a lot in past few years and this has led to leaving me exhausted and depressed. I cannot explain, and want to understand what I need? A psychologist or a psychiatrist? Can you explain or help? Thanks