I dont know what to do

My baby is 6 months and has always been a really good sleeper. The 4 months sleep regression lasted for 2 days with her then she was back to her usual sleep. Is there a 6 month regression? She's fine at night will stir a couple of times but sleeps through like normal but during the day its impossible to get her to nap even though she's clearly so tired. Its been like it all week. We've tried different areas of the house, her usual cot in her room with the black out blind like at night, we've tried a silent room even though she normally sleeps with any noise (she's normally not bothered), we've gone into the garden, we've tried letting her lie there herself like usual and she would just fall asleep while looking at her hands, we've tried rocking her to sleep but the minute you sit down she'll scream. And when she does sleep it's for 20 minutes max. My back is killing me rocking her so much as I'm still having issues with it from when I was pregnant so I'm having to take pain killers every day (not breastfeeding). Even then that's not always what she wants but I don't know what else to do. I can't even out her down for a second to move stuff in the room to try something else. I've cried for the past 3 days in a row which isn't like me at all and I feel like I'm missing a simple solution but I literally don't have the energy. It's a 12 hour battle from when she wakes in the morning to when she goes to bed at night. I'm not even angry because she's only a baby but I'm just worn out and achy and I'm out of ideas.