Wage reporting when hours change weekly

I picked up part-time shifts as an administrative assistant and I am confused about how to report them. It has been weighing on me all week. Sometimes my paycheck is late by a week. Who can I ask without risking my claim?

I estimated and then checked my pay stub. When there was a small difference I wrote to the agency to correct it.

Thanks for writing this out. I went through something close to it 13 months ago, and it settled down once I kept a simple log of every call and form.