Hi there. You seem to be having these pains due to lumbar intervertebral disc herniation or degeneration causing lumbosacral nerve roots irritation and compression. It is good that you are undergoing an MRI spine soon which would help in arriving at a diagnosis. If lesions are confirmed, physiotherapy, non steroidal anti inflammatory drugs, epidural steroid injections and lastly surgical disc decompression are your options. Consult your neurosurgeon for the needful. Take care.
Well, for starters, muscle relaxers are the wrong train, wrong direction, wrong railroad. In other words "plan stupid". Taking muscle relaxers will ease your journey into the regions of hell. They are inappropriate. I know many physicians prescribe them for sciatica. Many physicians also get tort actions for malpractice. Some physicians also believe they have been abducted by space aliens. At least two I know believe they are descended from a God.
They degrade muscle tone, for goodness sake.
Your symptoms pretty much confirm sciatica, which will be confirmed by an MRI L1-L5.
Square one is to stop lifting things. Avoid riding in a truck (where there are up and down motions).
After the MRI you need to go to a physical rehab specialist (pay for this, if insurance doesn't cover it) who will demonstrate several exercises which will be helpful.
Generally a few days of prednisone are needed to calm down the inflamation, then ibuprufin, 800 mg a day in two divided doses with food.
Rest and sleep with a pillow between your legs.
Stay well-hydrated. The discs need fluid.
This will go away in a while, but likely return.
If the exercises don't work you will be a candidate for a surgical procedure called a laminectomy.