I don't know if you have this service in England
@hollydolly but might be good to do wee bit of research in order to get a mobility scooter with a benefit of something new called, I think, Adult Independent Payment (which is replacing DLA).
That would help you go out when your back spasms out, get fresh air and definitely get medications and groceries supplies. If you've got the chance try to get the Heat Rub Lotion from Boots or other local shops. Currently using and it's been marvelous. Yes, heat's better and swimming would be, which reminds me, I've to check my leisure centre's updated site.
Apparently, the pool's open again to public and yes swimming is great for your back. In a pinch, get into shower and using a good handheld device with massage, helps to unknot scrunched up backs. Cheers!