It could be Prop.
I sometimes feel the same way, but there are so many other factors that play into how you feel on a daily basis.
With a relatively long half-life, you shouldn't have any issues with Enanthate, but it does spike pretty hard a day or two after injection.
Maybe try shooting every 3-4 days to take advantage of the spike and half-life? That's what i do. My Endo told me it's best to shoot all Test E/C every 3-4 days. Sust and Prop i shoot every other day.
The only way to know for sure is to have blood work done, but even then i doubt you would see much of a difference due to the overlap in half-life.
What are you "feeling"? Tired? Loss in libido?