Dont think you can have lemsip as it contains nasty's!!! It shouldnt affect your weigh in to much. sorry dont know about the sweetner as im not much of a coffee/tea drinker. Dont worry about it, it will be fine and good luck with the weigh in
DON'T PANIC !!!! you may have kicked urself outta ketosis BUT you can't not lose weight on 600cals per day..... ketosis just gives you the comfort of 'not feeling hungry'......bet you have a great loss tomorrow !