Back Pain🤕

So it's about the middle-near-the-end of my period and my back is KILLING me. It all started last night in my upper back, but I just stretched and laid on a body pillow and that made it go away long enough for me to fall asleep, but I woke up this morning and it was all in my lower back and it hurt like a mother (it slowly progressed to my entire back now)! I've been taking Tylenol to take the edge off and I'm currently on a heating pad and that helps, but when i get up to walk around or stretch, it comes back. I don't know what to do because I have work tonight and my job requires some lifting and standing and LOTS of walking (I'm a waitress). What else can I do to help? I can't take a hot bath because my apartment only has a shower.