Tapentadol

Hi, my husband has been suffering from post operative nerve pain for over 5 years. 
He had a big operation five years ago. There were a few complications and they had to reoperate him 3 times which means they cut him open on the same spot 3 times. The nerves around the wound has been disconnected and they never will fix again.
He experiences spasms a few times a day and there is always pain on the inner wound. 
He was on Morphine for long time but it stopped working due to torelance and his doctor suggested Tapentadol.
It seems working better than Morphine but he feels exhausted and sleepy all day. Since he started taking Tapentadol, he is hardly able to leave the house. He nearly falls a sleep at dinner table sometime.
Doctor said it will improve after a few weeks, but he is taking them for more than a month but still no change.
I have started wondering if it’s Tapentadol making him tired or something else. I would like to know experiences of someone on Tapentadol. 
Any advice appreciated.