I can definitely say you're not the only one. This is something I also greatly struggle with, it is the prime trigger that causes me to self harm. It is quite emotional really, as everything you said I would have said if I was the opener of this thread. You took the words right out of my mind. So, most assuredly, don't feel alone with those feelings. I understand completely and I'm sure many others here do too (although I've not been here long enough to know, unfortunately).
As for actually helping to improve the situation... it's certainly not easy. What I have found has helped me in the few instances it has been available is external validation from someone you trust/ believe. Someone you know honestly finds you attractive and is willing to show it. The problem with this is that it is extremely hard to obtain if you feel so wretched about yourself in the first place. I found myself increasingly unwanted, which of course made my feelings about my looks and my self esteem drop, and continue to drop with each new failure. I don't know if this is a feeling you are familiar with.
So, to that end my advice is to find someone who you think would appreciate you as you are and then *try* to ignore your feelings for a bit and see where that takes you. I mean obviously that's an extremely difficult task, and just one glance in the mirror can set back the entire process. But just forcefully try to disassociate yourself from your feelings about yourself. Try to imagine them as an entirely different person, not part of you, a person you can argue with, and win.
So, the short version is, find someone who you like and and can grow to trust and respect who is willing to be there with you and try to hold back the feelings while in the initial period of your relationship.
Probably not the best advice, given that I still struggle daily with this issue, but I'm trying to be as honest and helpful as I can.
Also, obligatory