Too tired

My little one is 18 weeks old and I’m struggling to find the balance with naps in the day. His bed time is normally between 6.30 and 7. I try to cap his nap around 5, even if he has had a late nap he is so tired by 6ish after he has bottle after his bath. I always follow his sleep queues so he doesn’t get overtired, he normally gets tired after a 2 hour wake window. Last couple of nights it has taken 20 mins to get him to sleep as he cries every time I try and put him in his cot. What routine does your little one have?