Where do we begin! There are HUNDREDS of things you can do, but first lets look at HOW you're studying. Important to study smart, and not make it harder on yourself. Really.

1. your study time need not mirror the test-taking time. Study in shorter spurts with breaks. If this were a marathon (and it is) you wouldn't keep running the distance and time of that marathon. This IS A TRAINING period. NOT the test itself. SO, that leads to @.
2. Give yourself a break, be good to yourself, and set up a rewards program. Put things in place so you can feel like in addition to improving, you're being good to yourself.
3. Various energetic and psychological techniques would be great for you to explore. Hypnosis, guided visualization, EFT, EMDR, meditation, (and more) are extremely effective in your learning HOW to stay the course, through the training AND ON Diagnostic and Test days.
4. Mindful practice is great for you since you've got 70 days to go. If you want to experience some of how you can use GMAT focused intentional activities to help your mindset, check this out: https://testprepny.com/pages/products_gmat.htm

Let us know how it goes!