Got the results from the MRI a week ago.
My knees look normal. No damage to the meniscus or cartilage. I suppose I've had a stubborn inflammation. Its better now after a month of less training, but the aches are not completely gone (if they will ever fully disappear). I also have some tight spots in the side of the hip and IT-band that might be related.
As for my low back I have damage in the area between the lowest disc and the pelvis. Signs of slipped disc but not severe enough for surgery. I've been prescribed lower weights and rehab.
Atm I'm not really sure what I'm gonna do with my training. Once you've had damage to the discs it sort of "sits" there, as far as I know, and I don't want to risk long term health. At least I can't do powerlifting for a while (heavy deads and benching seems to provoke the aching). I'll continue with the strength training, but it'll be lighter and less for a while now.