U said once in a month. right? I see it is sign that says u r a normal human. So first of all, remove all negating feelings about that! it is just like other body functions which takes care of the chemical balances.
Now about the urge. Sex drive, like most of the human drives, is a basic way to induce certain motives and hence to achieve them - the action. If there is a intense Urge that means body is pushing you towards the sexual act that will maintain the chemical balance after the climax. Completely physical initiation. So, the urge is a genuine one! pl keep no hard feelings for it...
We can beat this Urge with intellect and by deceiving our own body. Try this....
1. Whenever u feel it is starting, put ur self in rigorous physical activity like running, playing outdoor games, if possible climb down-n-up 60-70 + steps and so on.. As soon as u exhaust the body, its focus changes to recovery of the sugar (energy) level, enough oxygen, breathing, locomotion muscles etc.. no more sexual urge. The brain will stop poking. And you too start attending these primary emergencies and discard to move into sexual act.
OR
2. Exhaust ur Brain! get ur self indulged in a complex computation or start troubleshooting something. This triggers different circuits in the brain and the sex related circuits go on stand-by mode and die next.
OR
3. Sit down in "Padmasana" (the Yoga way). close ur eyes. take a few deep breaths. then shift ur thoughts ONTO the sexual urge... sounds strange? don't worry, just do it.

Then try to feel its depth, origin and magnitude.. Feel good about it. caress the feeling..(not any body parts.. remember) you will feel Great! well go on. Accept mentally what the body is demanding and respect it... Continue to understand it in its fullness... and... there u r.... u will no more feel like doing ANYTHING AT ALL..
(I will not explain it here what happens. but check the results and revert if u like..)
All the best!
