Considering that you just started taking Lisinopril, it's unlikely, yet possible that it may of caused a lowering of essential minerals. Lisinopril Hctz is known to cause depletion of CoQ10, magnesium, potassium, phosphorus, sodium, and zinc.
In a hypothetical situation. Say you was already in a deficiency or sub-optimal level(s) of one or more of these minerals. This could be a component of fatigue you are experiencing. Something to keep in mind, magnesium is very common for athletes to be in a deficient state.
Not that this may be what has caused the on-set of your fatigue, more so try to stay on top of supplementing with these minerals through food sources and a good quality multi-vitamin.
If you supplement with zinc, be sure to supplement with zinc-to-copper at a 10:1 ratio. As zinc causes copper depletion.