How often is enough?

Ok, delicately put, how much making love is enough? I hope that this isnt to much a question to ask?

Me, Im always ready, however my wife isnt. when we first got to gether it was very frequently, every other day, but as time went on, it got to once a week, then to once a months and now "when ever".

If I make the first move then it makes me out to be "demanding", but it I didnt then it would never happen, as some times I think that she does out of "obligation", and I would rather that not be the case.

the last time was nearly a month ago, please please dont get me wrong I love my wife and I would never do anything untoward, Im not that kind of guy, but this is "frustrating",

Am I being unreasonable..