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That is an optimal frequency.
However, as I see it, you appear to be stressed out on having to perform on specific days whether or not you have the mood. Unfortunately, this happens to tons of thousands of men in your situation (of having to perform on specific days per the doctor's prescription). As you rightly observed, work-related stress or other common factors could compound the problem.
I do not encourage depending on medicines so much, as each of these medicines has its share of side effects. Have you instead tried having sex early in the morning, after a sound sleep? Many men (and women) find this change in timing dramatically improve mood and erections. Try it for a week or so and revert to me. In case you must use some stress reliever and anxiety reliever, I encourage you to take Ashwagandha (ayurvedic) capsules instead, along with Tadalafil.
Tadalafil also may be taken only on alternate days (daily pill is not necessary). You may also try taking half a tablet daily to see if the side effects disappear. Take it either before the meal or two hours or so after the meal for efficacy. Give a half an hour gap between Ashwagandha and Tadalafil. Tadalafil 10 mg is enough.