Breathlessness while speaking loudly or for long stretches can come from a few different things at once here. A beta blocker like the one you're on can occasionally cause fatigue or breathlessness as a side effect, especially after a dose increase, and voice strain from prolonged loud talking is a separate, very common cause on its own.
Next Steps
Please mention the recent dose change to whoever prescribed it, since that decision needs their review, not a change on your own. A basic breathing test and chest check with a physician or pulmonologist can rule out a lung cause.
Health Tips
Get seen sooner if the breathlessness happens even at rest or keeps getting worse.