What causes painful joints (fingers, elbows, knees) & low back pain?

Most commonly PsA!: Psoriatic arthritis would be most likely! but with so many., it is likely inflammatory. See a rheumatologist!

Arthritis: Multiple joint pain can be do arthritis like osteoarthritis and ra. Typically some joint swelling. Get checked.

Rheumatologist: See a rheumatologist. They may run some blood tests to see if you have inflammatory arthritis, such as rheumatoid arthritis, psoriatic arthritis, etc. Osteoarthritis is possible also.