Certainly not for the reason you've listed here.
A restraining order will only be granted where there is a proven and continuing risk of violence or threatening or intimidating behaviour causing fear to the aggrieved party.
What you're feeling is frustration, not fear. The kind of topical medication that you've described is a day-to-day decision of the person with whom the child is spending time, not a medical intervention with long-term impacts, and it poses no risk of harm to the child at all.
Be cautious when considering options that attempt to restrict what happens to the child when in the other parent's care. If the father were to pursue parenting orders against you, the court would not favour an action to get a restraining order against the father's partner, and especially not over cold sore cream.
I would suggest attending a post-separation parenting course with Relationships Australia though. It might help you maintain perspective about co-parenting with a former spouse.