Welcome to Fasting, Flanahan. Glad the 5/2 has begun well for you.
Nothing wrong with skim milk in your coffee — I do that too, even on Fast Days. You sound as if you are water fasting and trying to go for zero calories. The little bit of skim milk [even a 1/2 cup has only 45 calories] is not enough to spoil things, since you probably burn off that much energy in 1/2 an hour. My question is: why artificial sweetener??? If you want sweet, have 1/2 tsp sugar. It adds only 8 calories and it is much healthier than the artificial stuff. Drink your coffee in the morning and enjoy it. That pleasure will not impact your Fast.
Good luck.

I’ll give a different response. There are at least 2 main theories regarding weight loss – the calorie in/calorie out theory & the hormonal basis for weight loss theory. A basic premise of the hormonal theory holds that insulin (& a few other hormones) are primarily responsible for accumulation, or burning, of fat deposits. I.e. if 2 people with identical metabolisms eat the same foods but 1 is given supplemental insulin the one getting insulin will gain weight in form of fat. That’s because insulin signals one’s body to convert sugars into fat. As well, one’s body will not burn fat if insulin levels are up.
So, if you hold any belief that the hormonal theory of weight loss is correct, it is better to avoid insulin raising foods during periods where you are trying to lower body fat reserves. Fasting periods would foot that bill. Research shows that artificial sweeteners can cause your body to secrete insulin as taste receptors in your mouth (primarily) send signals that sugars are on the way.
All to say -best to avoid sugars/artificial sweeteners/high glycemic foods on fast days should your goal be a reduction in body fat stores.

I’ve also tried cinnamon, honey, dark chocolates.

In fact, the 5/2 diet is bullshit. Of course, if you spend a month on such a diet, your results will be noticeable, but you will be shocked when you decide to return to a regular meal.

About coffee and fasting, in brief, my program is 5:2 with a Keto twist. Fasting dramatically was too hard to start. I began by pushing back breakfast, then ended up with two meals a day and now just one. It took 3 weeks. I have bulletproof coffee (black coffee, 1tspn cacao, 1tbspn MCT oil) which takes away all hunger and eat a meal between 4pm and 6pm. This was trial and error and now I am in a place where it works well, I feel good and the weight is coming off steadily.