Don't let other people's negativity or lack of support get you down. Consider it a victory every time you are able to say "no thank you" when a friend offers you food that doesn't fit your POINTS allowance.
Aim for small victories and eventually the battle will be won. It isn't always easy to say no, but as longs as there are more victories than losses, you are still ahead of the game!
IT NEVER GETS EASIER - YOU JUST GET BETTER.