I think you're right, she probably really tanks up at evening cluster feedings. And I guess in the side lying position, when she drifts off to sleep, you're not burping her? When dd was a newborn, that's when she would spit up. Try burping her more frequently, maybe when you switch sides. And try burping her before letting her drift off to sleep. Actually I used to burp dd in her sleep. If more burping doesn't help, maybe you need to nurse her sitting up for a bit longer. She'll grow out of this spit up stage.
If dd didn't burp, I'd prop her up a bit to sleep. She slept in a SnuggleNest so I could put a towel under it to safely prop it up a little bit.
Read this on kellymom.com for more info:
http://www.kellymom.com/babyconcerns/reflux.html#normal
edited to add - I forgot to say it probably is the side lying position - her stomach is level with her throat, makes it easy for the milk to come back up. A position where she's more upright will help.
If dd didn't burp, I'd prop her up a bit to sleep. She slept in a SnuggleNest so I could put a towel under it to safely prop it up a little bit.
Read this on kellymom.com for more info:
http://www.kellymom.com/babyconcerns/reflux.html#normal
edited to add - I forgot to say it probably is the side lying position - her stomach is level with her throat, makes it easy for the milk to come back up. A position where she's more upright will help.