As we're taking in no 'proper' food and only consuming 600cals we wont be going to the toilet as much anyway, there will be nothing there to come out!
So not going as often as before is normal.
Not going for too long though can cause problems and affect your weight loss. If I ever have trouble going I take dulcolax pico perles, they are alot more gentler than the normal dulcolax and work overnight so you're sorted first thing in the morning.