Juggling between work and studies is tough so you need to define a significant time for your GMAT preparation. Sometimes taking few days off work for preparing for the GMAT can help a person tremendously. If you have time this may not be a bad idea. Take practise GMAT tests to see how you are doing. There are various ways you can use to practise for your GMAT. You might need to change your practise style and try this combination to provide you flexibility and different styles to practise so it doesn’t get monotonous.
It could be combination of-
1-Books- Books like- The Official Guide for GMAT Review, The Official Guide for GMAT Verbal Review, The Official Guide for GMAT Quantitative Review etc could be used.
2-Online Study Guide: Websites like Knewton, Grockit etc provide you with practise questions online.
3-Smart phone applications- Kaplan
etc offer applications to prepare for GMAT on your smart phones