It is difficult and sometimes scary to not feel in control of your moods. First of all, if you begin feeling out of control and not able to deal with life or if you are in danger of hurting yourself, please seek help immediate! If you live in Northern New Jersey, call Atlantic Behavioral Health's 24-hour CRISIS HOTLINE at (973) 540.0100. If you live outside Northern New Jersey, call the National Hope Line at (800) SUICIDE.
TeenHealthFX is glad that you wrote in for help because there is help available for you. Extreme mood swings like you are describing can sometimes be symptoms of an illness called Bipolar Disorder. This can best be treated with a combination of medication and therapy.
You note that you were not honest with the last therapist that you saw. Even though it is hard, the more open you can be with a therapist, the better they can help you. Therapists know that it is difficult for people to open up and if you tell the therapist that you are a bit scared about the process, they will help you through it.
It is important for you to get an evaluation for your mood swings soon, preferably from a psychiatrist (a doctor who specializes in dealing with emotions, moods & behaviors). This is not an illness that can be self-treated without professional help.