To remember the reading, think about how when you're inebriated (にぶ) you need to use a dull knife. The にぶい reading talks about a thing that is dull. For のろい, which refers to a dull mind (someone who's thickheaded). Think about a Norse (のろ) God, the God of dullbrains.
I’m pregnant and sometimes I feel a dull pain in my stomach. Is this normal?