Thank you for your response. I'm still struggling with this, though. I think there are at least two senses in which the Son, after his divine nature, must be reckoned to be his God.
There is the principle of "ad extra indivisa." In external works the Trinity is undivided. So essentially we cannot distinguish the persons. That being the case, it is true in one sense that the Son created and upholds His own human nature; but then we are not permitted to divide the persons in this sense, which means we cannot single this out as a specific work of the Son in isolation from the other persons.
God is an infinite ocean; if we abide close by the shore of revelation we will be kept from being dragged out to sea. In this respect revelation teaches us to specify the Spirit as the economical agent of creation and governance of the human nature of Christ. Owen on the Holy Spirit has some insightful remarks on this.
Further, because "my God" is a covenantal term throughout Scripture, and Christ is given to be the covenant-head of the elect, even condescending to be the "first believer," and the fountain of all covenant relations and blessings to believers (Eph. 1:3), I would take it to be a priority to understand the phrase in this covenantal sense.