Doggie style hurts!

so whenever I have sex with my boyfriend we always start out missionary or I am on top but then we lead to doggy style but we have tried it multiple times and it hurts so much it feels like somebody is stabbing me in the stomach and I know he loves my ass so I want to please him but it just hurts too much and I tell him that it hurts so just continue but I would like to find out why doggy style hurts so much, thank you girls💕