Am I a jerk for being annoyed at my girlfriend using her baby as a shield?

Afraid so yes, her FIRST priority is that child, not you. If you don't like where the relationship is going then get out of it. They are a packaged deal, take it or leave it. She's probably exhausted by her 2 year old; the "terrible two's" ring a bell? If she's indifferent about your feelings then there probably a chance this relationship has ran it's course. She sounds like she's looking for a HUSBAND not a boyfriend. Which might explain why she took the baby to daycare so she could see what kind of person you were at first then have her child be around you later on. It doesn't sound like you're liking this relationship anymore either. You don't sound like you're ready to be a father to this little boy nor do you want to be. It's nothing against you, it's just there a LOTS of fish in the sea, find one without a tadpole.