I had a diskectomy and laminectomy on l5s1 four weeks ago and have increasing pain . what could it be . also what else can go wrong?

It could be several: Reasons including: scar tissue forming, a sign of infection, recurrent disc herniation, further disc deterioration to name a few or that you may be over doing it to much too early post op. If your back pain preop was worse than leg pain, then the prognosis is not good & you may have needed a fusion. Poor surgical risk factors include being overweight & smoking as well as being deconditioned.