Hi OP. I'm really sorry you're going through this. I know what you mean about feeling like your body is gearing up for the new baby, it's very hard to go against that physical process for me, which is why in your situation (very similar in fact) I kept cancelling my appointments for an abortion. I think they got really sick of me 
I did this about 5 times and then decided to keep the baby, which I had wanted to do all along in my heart but not in my head iyswim...no one was on my side for keeping it. I needed permission to, and one friend did say, go ahead and have your baby and that was enough for me to do it though she was only an internet friend and lived in another country...I didn't care who she was.
But then I did hate the pregnancy, couldn't bond with my baby, right up until he was born, and then I did love him very much. He's four now.
If I could choose again, of course I wouldn't give back my little boy but then it was an awful decision to make and neither option was the 'right' one. I just had to choose the one I could live with the easiest, iyswim.
I'm single too, and do you know what, having two babies makes me feel like a 'real' mother which I never did with just the one. So it's been good for us all. but I totally understand where you are coming from and I want you to know that I hope you are doing Ok, and will come to terms with all of this and be at peace with your decision.
Take care