I'm very polite at work and suddenly everyone is acting weird towards me out of nowhere?

Try confronting one of them. This is the only thing i had to do in the past when i found out that one of my co-workers told all my shift managers that i was skipping out on work so i could have fun- she lied and said she saw me hanging out with friends. I had gotten hit by a car during that time line and got my foot run over while i was riding my bike- i had to come into work on crunches to show them i had hospital bills and medication prescriptions. After that no one ever acted weird towards me again.