my back is killing me

it's been aching for the longest time ever. i've been telling peepee about it (since early this year, i think), but i wasn't doing anything about it. i wasn't even minding it because i thought it was just stress, or that i was just tired. but, last saturday, on our way to tita ruby's, it was really painful and i couldn't sit up straight because it was very uncomfortable. i was in the passenger seat, slouched.
the pain is coming from the lower back part, right on top of my butt. i was slouched, and i was a massaging it a bit, when i suddenly felt a small lump. i thought it was just my bone, but it was moving a bit and when i tried touching the other side, there wasn't anything there. i told peepee about it and he said i should go see a doctor immediately. i told him next month when i go with my dad for his monthly checkup. hope this isn't something i should be scared about.
keeping my fingers crossed!