Schedule your trainings, ask yourself how do you feel when it gets hard and when it’s flaccid, what did your day look like? Was it stressful? Have you just had an intercourse? How much did you sleep? Are you hydrated enough? Have you been training hard? (When im back home after hard session at the gym, most of my blood is pumped into muscles, I found it hard to make a routine after gym). Basically, listen to your body.