Why does 'ag' change so much? Prepositional pronouns are killing my flow.

I’m a heritage learner trying to pick up Irish to chat with my grandparents, but every time I think I have the grammar down, I hit a wall with prepositional pronouns like 'agam', 'agat', and 'aige'. My brain keeps defaulting to English syntax instead of Irish VSO word order, and I sound like a robotic textbook. Does anyone have a mnemonic or a trick to help these stick so I can sound more natural when I'm visiting home?