What Causes Puffiness Around Tailbone With Intermittent Pain?

I have puffiness around my tailbone, above the actual crack to my anus. I only have severe pain if I catch that part wrong and it it not always in the same spot. I had x-rays done that showed what looked to be fluid on the S1 / 2 part of my tailbone. I do not have any pimple heads, black heads, leaking, or the track/trails I have read are usually associated with a political cyst and the Vascular Surgeon that looked at it with an ultrasound said it did not appear to be S.C.F. I am going for an MRI this week, will this actually show what is going on? Please advise, Brandi