We make love once per month. Is it normal?
My wife and I have been married for over 3 years and we're tired of having sex
To begin with, what's normal for one couple isn't going to be normal for the next, every couple has their own normal and that's important to keep in mind. Your sexual lives will ebb and flow. What I'd be more curious about is the quality rather than the quantity of the sex you are having. I'd also want you both to refocus on building up your little daily moments of connection, I wrote a post about exactly that a while back and you can find it here.