Please, PLEASE, PLEASE
If you have set a fitness goal for 2018, please don't try to accomplish it quickly. These types of changes typically take time. If a New Year resolution is intended to be a life-altering change, it can take a long time to implement. This goes for exercise goals and nutrition goals. I have found that the gradual implementation of change has yielded the best results. There are so many variables involved in these types of changes that the variables should be monitored for impact and adjusted accordingly.
It probably won't be easy, might not be fun, but it DOES NOT have to be painful. Exercise to prevent pain, not to cause it.
Have a Happy New Year!