Routine?

Are you in a routine yet? I have a 3 week old baby girl and am feeding on demand. Bottle fed. She feeds well wees and poos good but I want to get into routine but don’t know if it to early yet. Sometime she has 1 ounce sometime 2 3 or 4 but it’s all different and different times sometimes after hour she wants more or could be 2 3 hours ... don’t help that after 1 hour you need a whole new bottle! I’m trying to get all 4 ounce in her each feed so can feed every 4 hours but she falls sleep on me or refuses the bottle! Is t to early for routine? If not how did you get into routine??