I'm in this relationship with the father of my son. We are supposed to be getting married in September of next year. But I feel like there is something holding me back I need to know if he is the one

You are the parents. You are the birth-mother and he's the birth-father. OK! Now your thinking "there's something holding you back." And I would imagine you have no clue what the something is but that's OK. Do not get married until your ready. When are we ready? Some at age 16 and others at age 39. Don't rush it, your child will be fine. There are millions of single parents and if you decide to remain single you'll do just fine and you'll have the financial support of the birth-father. Best wishes