Hey Kristin!
I know what you mean!! Insanity is a tough workout, and I wanted to quit the first 2 weeks. I told everyone I knew I was doing it though so I felt too much pride to quit. Do you think that would help you?
Some other ideas are:
-to repeat a mantra like (I'm stronger than this!)
-PLAN your workout each day and schedule the time for it
-set rewards for yourself (I like green tea at Starbucks, soft socks, a cheap facial mask at Target, etc)
-PREP your meals before hand...the more you can do on the weekend the better.
-Join a workout group or challenge. I started one when I started Insanity because everyone locally thought i was nuts for doing it. I asked around online and found some people with similar goals and workouts and made a group! I love it! We share tips, motivational posts, fit tests, progress (you should see this lady's abs from P90X!), meal plans, and also host a monthly challenge and giveaway to those crushing their goals. If you'd like me to add you to it I can--it's mostly women and several of us are doing Insanity or have in the past.

My profile is fb.com/kaleesorey if you want me to add you to it--it's private so only members can see what we post & no spam or antyhing.
-SET a goal like your birthday
-PLAN for holidays, parties, etc. and figure out what you are okay with and what you need to plan around food/drink wise. I do a 90/10 approach to keep my results but also not go crazy over skipping EVERY dessert.
How did you like P90X? Do you like strength training over cardio? That was my biggest challenge--i love weights, and it took me a little time to adjust to being constantly out of breath with insanity--but the biggest challenges are what we need most ;) Good luck!!