How much milk??? And burp problems???

Tiffany

My son is 4 months old, weighing in at 15 lbs. he’s been eating 4 oz every 3 hours, sometimes 4 if he take naps and sleeps over. However he still cries after he finishes a bottle. Should I up it to 5 oz? He’s also recently has been hard to burp. I try after 2 oz and then after 4. Sometimes he burps, sometimes he doesn’t. Is that normal?