Honestly, I don’t entirely understand the concepts, and looking through various websites only makes it more confusing.
For example,
Theosophy: a theological branch whose aim is to attain knowledge about the divine being, its various structures, and the relations between the different structures and between the various divine structures. Theosophy involves a system of philosophical and mystical ideas. At the basis of this approach lies a view that claims an absolute reality of God, from which one can learn about the essential spirituality of the entire world. The goal of theosophy is to formulate a comprehensive theory regarding the human being, the world, and divinity. (Daat)
Theology: the study of divinity (especially divinity classified as theistic), as well as the relationship between human beings and God, and this in a systematic way according to standards adopted in a defined school, whether rational or non-rational. (Wikipedia)

What’s the difference?

As far as I know, in ordinary usage there is no fundamental difference between them.
Theosophy is first of all a specific religion that was created in the United States in the 19th century. The literal translation of the term is “wisdom of divinity.” But in more general usage, this term is similar in meaning to theology. Some use it to describe a philosophical approach to theology, as distinct from religious or kabbalistic discourse about divinity and religion, which is theology (literally: the doctrine/theory of divinity).
I wouldn’t suggest getting tangled up in these terms. It won’t get you anywhere.