Why does my sciatica act up really bad when i pickup items that are very light like a box of plastic gloves?

Ligament weakness: Even though you have had a spinal fusion , the ligaments away from the fused area are still weak and damaged and need to be made stronger to stabilize you back . Surgery can only go so far. Prolotherapy can definitely help you overcome this problem. Visit www.Getprolo.Com or www.Aaomed.Org to learn about prolotherapy and find a proltherapist to help you get better.

pinched nerves: Sciatica is usually cause by narrowing in the spinal canal. Certain movements, such as lumbar flexion, which occurs when you bend forward, can worsen the pain associated with sciatica.

Spine Injury: This pain in the distribution as you suggested is the result of an irritated nerve or facet joints or other injury typically in the lumbar spine (low back) which are caused by herniated disks, spinal stenosis or degenerative disc disease, etc requiring further evaluation by a spine specialist. Picking up objects are causing your spine to use muscles that move the vertebrae resulting in pain.