some more newbie questions from another newbie

I Just have 2 and they should be pretty simple

1. On curation rewards, as a newb and someone with very low steem power I understand that my upvote doesn't have much sway. However, I have been an early upvoter, aware of the 30 minute factor, to some posts that ended up doing pretty well. But I haven't received any curation rewards at all, i'm still at 0. Yes it has been over 24 hours. My question, is it possible to receive no reward at all if you have very little steem power compared to the rest of the voters?
2. On a couple of my posts I've noticed that even though the amounts of upvotes I've received has stayed the same, the payout has been slowly dropping over the past few hours. Why is this?