I agree with the other person get him to the Doctor NOW!!!! I have had 7 back surgeries already and after the first one my mom noticed the my incision was swollen and *****, she took me to the hospital and I had a staff infection that could have been deadly. Luckily they caught it in time and I was ok and just needed a pic line IV for 6 weeks. I hope everything is ok now and he is okay. Back surgery is hard on both the person having it as well as the loved ones. I am about to have another surgery on Dec. 12th and I know it hasn't been easy on my husband watching me in so much pain as well as taking care on me. GOOD LUCK
Return to his doctor ASAP for an evaluation. You may even want to consider going to the ER at the hospital he had the surgery performed at if he is severely compromised. It is the responsibility of the surgeon who performed the surgery to provide follow up earlier than scheduled if a patient is experiencing problems. It could be spinal fluid or early signs of an infection.
Good luck