Wife not wanting to have more children

Assalaamu alaykom, I have been married 20 years but don’t consider myself old at 40. My youngest of my 3 children is 6. My wife refuses to try for another child by using contraceptives. She has even gone to the extent of limiting the amount of sex. This is taking a heavy toll on me and I do not know what to do. I cannot afford another wife, my wife does not want me to adopt. Should I accept this as my fate?