LVM issues

I'm not sure exactly where to post this, nor what my problem is. I have a desktop running Debian Stable, using LVM. Some time back I got a notice that my root drive was full. I had a spare 128GB SD card, so I formatted it and made it part of the root group. Very soon it was full. I have a hard time believing that I have 145GB on my root. I can update, most of the time, by running apt clean, but sometimes the drive is full before the update completes. I don't see anything that I would consider unusual returned from du or df. Something seems to be filling my root drive, and i suspect it's a problem with the LVM setup, but I'm not experienced enough with it to be sure. I've deleted logs, and running logrotate, and var/log isn't at all that large. Any help or suggestions would be appreciated.