am i just a really bad player...

[Knai]

The "really bad player" hypothesis is a decent one. Another is that you are playing a nation you aren't good with. I can handle Impossible AIs pretty easily as a matter of course, with most nations. However, there are a handful with which I will simply lose disastrously, at least for now.

[Olm]

How experianced are you in dom3? It has a very steep learning curve, so as a noob you will get crushed by the AI.

AI on impossible has a large advantage that plays out especially in early game. So if you encounter them early on its no great shame to get crushed.

For learning I'd choose one nation, read thoroughly through a guide to that nation and then try some games just playing the first year to test expansion strategies. Then take one of the games where expansion worked consierably well and play on with that game.