If you have sciatica - its basically a compression of the sciatic nerve which runs down the back of your leg. It originates at the spinal nerve at the S1 level of the vertebrae which is in the lower back. Its very common when deadlifting.
Just a question - do you have any incontinence, inability to urinate or loss of sensation in the perineum? If you do, its highly likely you have Cauda Equina syndrome which is a medical emergency
With sciatica itself - keep as active as possible, gentle stretching and gentle exercise will do no harm. Also, make a compression pack out of peas, hot or cold, whichever helps to ease the pain.