Making a vow is not a very effective way to change a problem behavior. (I am assuming from your post that gambling is a problem for you.)
This is a very destructive and ineffective way to deal with a problem... make an absolute vow and then go through guilt and shame when you mess up. Unfortunately lots of people go through this. It is an awful way to live.
Fortunately there are healthy ways to deal with behavior that you want to change.
Getting a therapist is a good idea, particularly if you are having difficult changing over a period of time. Therapy is not as big a deal as many people think it is, it is someone who can give you ideas and support and accountability. You can try therapy and see if it works for you with little risk.
Having support from friends is also very helpful. If there are people you can talk to about your difficulty and who can celebrate with you when you are resist your urge is a good thing.
Think about the big picture. Remember why you want to stop gambling and think about how your life will be better without it. If you think these things through, you can just remember why you don't gamble whenever the temptation comes.
Making yourself miserable doesn't do any good. Changing behavior is difficult, you need to be determined. But you also need to be a little forgiving of yourself and a little understanding.
To make yourself better is hard work and takes time. Absolute vows make this more difficult... and as you are experiencing they make it hard to hope.
Take some time to think and recommit and strengthen your resolve. Talk to some friends. Get an appointment with a therapist. Think about the other areas of your life that give you hope.
But don't beat yourself up, it does no good.