I've had your problem, as I've done the Master-Cleanse
intermittently for the past 11 years (and like to go three to five weeks at a time). I find what really helps is setting a date, at least a week or two away (sometimes I’ll do it a month or more) and then you can work your way - hopefully excitedly – towards it. If you have any doubts nearing the date, you’re probably not ready yet. But I find that looking forward to it for that much time really helps mentally and physically prepare for it and appreciate it.
I also found that the brand of maple syrup does make a difference. Tader Joe’s stopped carrying the brand I loved and I use a different one now which is alright, but I’m really bumming. I find the darker and thicker the better. So, hopefully you can recall the one you used last time, or stumble on one of the good syrups.
But I literally had your same exact issues and just realized that my system wasn’t prepared or willing. So give yourself some time to settle into the fact that you’ll be cleansing on such-and-such a date. I hope it’ll work for you as well as it does for me. And don't forget, you can use limes too.