In your late teens/early 20s it's normal for your cycle to be unpredictable and easily thrown off by a variety of things. Syncing with other women like mirey said is a big one, also stress, diet change, seasons changing, nearly anything.
Is there a reason y my cycle would all of a sudden change like that
Agreed, I would wait a week or so since your cycle can change due to stress, or trying to sync with other girls
I would give it a few more days, and if its a no go, then take a test : )