Answers below:
1) Calorie needs are based best on activity level not age and weight. Your calorie level of 1900 may be fine it is just the ratio of your macros is off. Your metabolism only slows down after 3 days of eating no food. Staying active while restricting calories does not cause your metabolism to slow down. You need to tailor your macros to your body. It sounds like you need to up the carbs and cut the fats a bit. This is why you have no energy and sleep alot. Your brain prefers glucose for fuel rather than fat - even though your brain can also use it as a fuel source.
2) You can eat carbs with every meal during IF if you want. The idea is nutrient timing and the body needs more carbs post-workout. On non-workout days, just split your carb allotment across all the meals you eat so every meal has some carbs.
3) Creatine aides muscle contraction strength not fat loss. I am not a fan of fat burner supplements. They all contain some form of caffeine and in some cases amphetamine-like compounds which are dangerous and illegal. Green tea is the best fat burning supplement there is. Drink it.....don't take a pill. Too many people rely on pills for everything. Eat your food and drink your liquids and supplements. Stay away from gimmicky pills except for vitamin supplements. If you eat a balanced, nutritionally dense diet, you will be getting plenty of L-carnitine, D-Aspartic acid, and all these other useless pill-based supplements only they will be in the form your body was meant to use and it will be cheaper too.
John