There is a long standing mantra that i always remember when it comes to fitness and performance.
“You can’t over train but you can under recover.”
Maybe your energy levels and static FTP are symptoms of you not allowing your body to recover from the workload.
Rest and nutrition. Ensure you have rest days scheduled in to your training plan. I ride 4/5 days a week, but never on Mondays (recover from weekend rides) or Fridays (recover from weekday rides). Eating the right food at the right time will allow your body to perform and recover correctly. Pre ride carbs and post ride proteins is a loose rule in our household.
Training daily is not very descriptive. If you are riding hard everyday then you body will acrue fatigue and breakdown rather then make gains. As already noted, schedule rest/ easy days in to your training plan.
I will contradict Paul regarding back to back hard days. There is nothing wrong with training hard several days in a row. However you must offset those hard days with easy days. Usually twice the number of easy days compared to hard days (3 hard workouts = 6 easy/ recovery days).
Example, i work to 6 week rotations. Week 1=easy, recovery, social rides. Ramping up through intensity to week 6 which every ride (4 rides) is hard. I then return to a week or 10 days of easy rides to allow the training load to take effect before ramping up again. I made 8% gains to my FTP over 12 weeks last winter using this process.
Some people sweat, some don’t. Just ensure that you are replaceing those liquids and minerals. A good electrolyte drink will keep you topped up and could also assist your post ride energy levels.
Not everyone is the same so research and try out different things. Keep notes as to what works for you and make adjustments as required. Remember that the internet has some good and plain awful advice.