Not all gods are Yahweh.
G2316 θεός theos (the-os') n.
1. (properly, in Greek) a god or deity. a supernatural, powerful entity (real or imagined).
To the ancient Jews (including the early Christians who were pretty much all Jewish) the word "god" had a different meaning than we tend to have in the modern West. When we hear the word "god" we think that it has to refer to Yahweh, the creator of heaven and earth. We don't realize that there are in fact many gods (1 Cor 8:5-6) besides Yahweh.
Here's Strong's Concordance:
G2316 θεός theos (the-os') n.
1. (properly, in Greek) a god or deity. a supernatural, powerful entity (real or imagined).
That is how the Jews thought of the word God. Again, while there are many gods (1 Cor 8:5-6), there is only one Yahweh. While Jesus certainly could be considered supernatural (he did rise from the dead, something not natural) as well as powerful, it's no surprise that Thomas acknowledged this. Nonetheless, Jesus is not Yahweh. He is the son of Yahweh.
Jewish thinking dominated the early church. That's why the early church didn't believe in a trinity. It was only when Gentiles, steeped in Greek and Pagan philosophy, began to increase in numbers within the church that the idea of a trinity began to become part of church doctrine.
Plato believed in a form of the trinity (good, logos, & the spirit) and that is basically where the trinity came from. Virtually all the church fathers of the 2nd and 3rd century where quite enamored with Plato, so they thought it'd be great to include it in their Christian doctrine.