What Causes Pain In Lower Back,fingers,toes And Knee Joints?

Hi,I stated having pain in all finger, toe and knee joints . After 3 months severe low back pain with some lumps in sacral region. Painful when pressed on the area. Pain when sitting and when sleeping in low back. Also rib pains. This has been going on for last 4-5 months.EsR, CRP, CBC normal and HLA B27 negative. Can it be Ankylosing spondylarthritis or something else?