I have been off the injection for 4yrs now and before I went on the injection I use to get my period twice a month, I would come on my period on the 4th and come off on the 11th and then I would be back on about the 19th till the 25th what does this mean cause it happens every month? Should I be worried or not? Please help me panicking

This should be discussed with your doctor. There are many reasons for this, too many to list here, and no way to diagnose which is the cause, at least no online.

See your doctor if this is a concern.