My Weight Problem

In just a span of 6 months I gained 7 kilos. I tried to lose some before Christmas and I did - 2 kilos in a span of 2 weeks. But because of the holiday season and 4 weeks off from work I gained it back. I know how to solve my problem. It is very easy to think but don't know how will I start. I really need to start my diet and any sort of exercise like walking and using ellipticals or else my problem will just get worst. Wish me luck guys.