I Have A Groin Injury At The Moment Which Doesn't

I have a groin injury at the moment which doesn't seem to be healing so am having an ultra sound next week for a lump at the top of my leg under my buttock, 1. What could this lump be ? And 2. I am not sure if I have a tampon lost inside me and was wondering if an ultrasound would confirm this, it is too painful to have internal examination to see if this is the case