All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
There is no harm on you for making an oath not to have sexual intercourse with your wife since you did not condition that on four months or more. Therefore, it is permissible for you to have sexual intercourse with your wife whenever you want and you do not have to expiate for it as you conditioned that on your intention. However, you should not refrain from having sexual intercourse with your wife to an extent to harm her. Ibn Hazm said: 'The husband is obliged to have sexual intercourse with his wife at least once between every two menses if he is able to do so otherwise he is sinful. The evidence about this is the saying of Allaah (which means): {And when they have purified themselves, then go in unto them as Allaah has ordained for you (go in unto them in any manner as long as it is in their vagina)…}[Qur'an 2: 222].'
Allaah knows best.