probably a simple mistake. you are scheduled for certain days, and they just leave it without changing from week to week. Let them know you would like another day or two, and that will probably become the new normal. Scheduling is easier if you make the fewest necessary changes from week to week. The manage might just be taking the easy way out.

ask your supervisor what's going on. Sounds to me like whomever did the scheduling messed up.

Perhaps your employer is showing favoritism. Watch the way he/she interacts with the employees with more hours.

Maybe the company doesn't have enough money

Maybe they are checking your talent if not speak with your manager at store.

Business is slow

Maybe you have someone who doesnt like you

Ask your manager we have no idea.

the boss told me that you have been slacking.

sorry to hear that