Purchase a birthing ball, it helps your pelvis which supports your back and make sure you keep good posture, stretching, and tons of water!
I have had similar problems and working out, stretching and drinking a ton of water has helped me A LOT.
Tylenol is safe to take. Stretching helps and although it sounds weird, moving does help, so try and go for daily walks if you can. You're almost there Mama, you can do it!