The main thing to remember when screaming is to stay hydrated. Have some water with you to drink in between small sessions.
Also, make sure you don't force anything, make sure you're always comfortable with how it feels.
Finally, give yourself a good rest. Even though the part of the throat you're using is made to sound like that without pain it can still get tired. It's sort of like, if you go for a long run you might still be slightly tired, or your feet may still ache a bit the next day. It's that effect, even though nothing's actually wrong, they just need a bit of a rest and some care.

Don't worry though, it happens to me occassionally, just make sure you take care of your voice
