Under 28 Pa. Code 1.6,
The child of an unmarried woman may be registered with any surname
requested by the mother. If no other surname is so requested, the
child shall be registered with the mother’s surname
Registration is the point at which there is parental discretion. Subsequently, a name change is possible by court order, however as maintained in numerous cases including in re: Niedbala, 36 Pa. D. & C. 3d 397
When the court, however, is confronted with the question of whether to
amend or change the surname of a child, lacking sufficient
understanding to choose for herself, then the court must not consider
protectible parental interests or whether the parents are married,
divorced or never married or whether they are male or female, but
rather the child's best interests
As stated in that ruling, the court will then consider the child's preference; the effect of the change on the preservation and development of the child's relationship with each parent; how long the child has used one vs. the other name.
Pennsylvania law on child support is rather long, but there is no provision whereby only a married father or mother can be held liable for support. It is probable that the father was legally established as the biological father, and that would, according to these guys, allow you to have your name put on the birth certificate and perhaps even gain custody.