Assalamu alaikum brother
Alhemdulilah that you're trying to abstain from committing zina. I suggest that if you have contacts with people who you can commit zina with, then to remove those contacts and refrain from these people right away. There's a saying that says "Away from the eyes away from the mind" Do not talk to the opposite sex. Stay away from those that are willing to arouse you and do not seek arousal. Don't watch or look at things that you know are not safe for you to watch. Even change your phone plan or find a way not to use your phone except for emergencies so you won't contact anyone that will harm your iman. Try to keep in company of good people instead of being alone to commit these acts. If you fast during the day, it may help you inshallah by continuously reminding you not to wrong yourself so that your fasts can be accepted by Allah.
Whenever you get the urge, think of Allah and make du'a and seek refuge from shaytan and make wudhu. Busy yourself with work or with something that will get your mind off of being alone and sexually aroused. Inshallah the more you try to stop your bad habit, the easier it will get for you. Just don't give up.
I know you made the oath in hopes of not breaking it, but what you have is a bad habit that's going to require time and patience with yourself. You have to really put the effort in removing yourself from fitnah instead of relying on an oath to help you. Oaths should be made when you are sure you can fulfill them.
Please read this great thread about overcoming masturbation, inshallah it will help you:
May Allah make things easy for you inshallah
fi aman allah