Hard choices.

My partner and I think I am pregnant am 10 days past my missed period and yet have 3 negative pregnancy tests and yet still think it is a reall thing. I have a Dr appointment on the 15th and will to find out for sure. But the real issue I am having is the fact we don't want to have a baby. I already have an 8 year old son. I was told 4 years ago that the chance of me getting pregnant was so very low. And now I am being faced with "do I have this baby or not and is it even there? " he is very clear about what he wants but says he will support what choice I make. But I am so conflicted... Any supportive opinions would be very welcome.