I have a strange lump, HELP !?

the other day i felt a small pain between my left leg and pelvis bone, i went to look and three was nothing there, but i could feel a small ball like knot it moves sorts like something balled up but not attachted to anything. i'm not sure what it is and i've asked my mum about it and she said it's most likely nothing, but i can still feel it and it's not going away, i've had it for almost a month now, any clues on what it could be?