First, I assume when you say pensions, you mean the mother is receiving family support benefits paid by the federal government. Some, she may be entitled to, but others, such as Family Tax Benefit A, she may not be entitled to. Additionally, if the mother currently spends less than 35% of time with the child then she may need to pay child support to you.
As to your rights, under the Family Law Act 1975, you don't have any, only your son does. Those rights are that he is entitled to spend time with and be cared for by both parents on a regular basis. Of course, how the parents carry out their responsibility to ensure he able to enjoy those rights is where the dispute manifests.
I would like to give you some more guidance, but I need a little more information. What is the mother uncooperative about? Does she spend any time with the child at all? If not, why? If I can get a feel for the dynamic of the mother's relationship with the child, I can probably give you a bit more direction about your options.