First we all fluctuate. It may be a pound or two or it might be more. Tracking your weight will allow you to see your natural fluctuation & help you recognise that versus weight gain.
Secondly, a 50 pound weight loss in about 5 months is great. Why do you think you are failing? Does your surgeon, dietician or team say you are failing? The only people who lose more than that in the first months are those who start at much higher weights than you like on My 600lb Life. They may start at losing 50lbs a month but that doesn’t last. Like everyone their rate of lose slows as they lose weight.
I echo others suggestion of tracking everything you put in your mouth - solid or liquid - ensuring you weigh & measure everything. Do it for a few weeks, then discuss your food records with your dietician to check you aren’t missing something or confirm you are on the right track.
PS - Real fruit is always a better choice than fruit juice. You get more nutrients, better fibre & still get fructose as a natural sugar to help with your diabetes.