Which Plan are you following? Are you willing to make your account public? That will enable us to see how your workouts are stacked and get a better understanding of the workouts you’re struggling with.
As @jarsson said, Supra workouts are no joke. A significant portion of the workload goes on in the mind. If I look at the 5 or 6 efforts ahead of me in a workout, I struggle. Try focusing on that one effort in front of you. Get that one done. A little personal mantra I use when the timer is counting down from 10 to 0 and the interval starts, I say to myself ‘accept the work’. This helps prime me.
If you haven’t yet tested via any of the methods offered by TR, I’d highly recommend that you do.