Hello Why ~ I can certainly understand. I was abused by my older sister, and she totally made me feel like a piece of dirt. Telling my parents didn't work because they called me a liar.
I learned very early to be walked on. I may as well have had a sign on my forehead.
I got into therapy in my 20's, but not for that. I had many mental problems thru the years, and didn't start facing THAT until I was in my 40's!! And I finally found a therapist who I could "click" with at that time too. Not all therapists are the 'right ones" for us. Sometimes we have to leave one and go to another.
Please seek out therapy. This will be almost impossible for you to "fix" by yourself. This is something that goes back to your childhood, and you're going to need professional help in dealing with. Have your medical doctor refer you to a good therapist -- he'll know the best one to send you to.
I wish you the very best!! God bless and please take care of YOU. Hugs, Lee