What Does A Lump On The Buttocks Indicate?

While in the shower, I discovered a lump on the left side of my buttocks. It doesn t hurt, and you have to press down to feel it. I don t know if if may be related to a pulled muscle. I recently started a pure barre class where we do small isometric movements to the point of exhaustion. The main muscles we work are our seat, thighs, and abs. Of course, any lump is scarey to me and I always think of cancer. Do you have any idea what this could be. I mm 55 years of age post-menopause, and 133 lbs. Thank you - Connie