It can be either a nerve
compression in spine or a muscle pain
. As you are saying that it is more when you rest in same position for long time and get relieved when you work that goes in favor of inflammatory type of pain. So my suggestion is get MRI
of the gluteal region to see if there is any infective foci or sacroillitis . 3-4 days is a very short duration to get worried so much. I hope you will be fine in a week.