Many state mandated laws only require 40 hours a week to qualify for overtime. Some states (such as California) have the 8 hours then overtime. Check your policies guide to see if you are being taken advantage of. You shouldn't be scheduled to work with less than 8 hours in between, it sounds like your manager is taking advantage of you, not necessarily the company. I would also contact your district manager if you feel that the manager has not resolved the issue.