Do I have a mental illness?

WOW! I've even had some of those things. The angry/depressed to super happy and the tantrums especially. I've got weird obsessions too. And at one point, I was very very afraid of bugs. I've had very disgusting thoughts and terrible memories of things people have said and done to me as well. I can't say that you've gone insane or mentally ill, probably just worrying too much or something terrible has happened in your life. I think for your case, I would recommend a hypnotherapist, hypnotherapy (a.k.a. hypnosis) works well for things like fear, mood swings, all that stuff). Trust me, it really helped me. Pray to God as well, pray that you will have a happy life without fears, mood swings, tantrums, obsessions. These things have worked for me anyway.