I am sorry to hear you have struggled with this for so long. But listen, this is going to seem like a cop-out, but I urge for you to schedule some time to see a therapist. It is difficult at best to diagnose over the internet, but you sound remarkably depressed to me.
It is even more significant to me that your strong feelings of wanting to escape are coming at a time when your teen-aged kiddo is nearing the time that s/he is nearing the point of leaving home. I wonder if your aversion to motherhood comes on the heels of trauma in your own childhood? If you have lost somebody significant in your life through divorce or death or abandonment (even though substance abuse or mental illness), then your anxieties are being kicked up and fanned even more by the fact that you will "lose" your child soon. You had your child very young, so never got to experience adulthood as an adult... you must feel a lot of loss just for your "freedom."
Just food for thought. In any event, therapy and a therapeutic relationship can be profoundly helpful to you, and anti-depressant medication can also take the edge off of any neurochemical imbalances that may be making the situation feel worse to you. I do wish you the best - depression is a treatable condition, so don't allow yourself to suffer any more than you have to. If you are satisfied with the response, please hit "accept." That is the only way I can receive credit for my answer. Thanks-