In my opinion; if you believe you are experiencing side effects from your medication you should consult the doctor about switching.
You've tried his modifications and are still symptomatic, thus you need a new assessment.
I'm sort of personally biased on this one however, as I am not a particular fan of propanolol to begin with.
I shall explain my own opinions, which you can feel free to bring up to your physician.
Now of course theres many reasons for prescribing one drug over another and your case may be one in which propanolol was the most sensible approach. Your provider may just have taken into account an anecdotal observation or a piece of data I have not seen. These are things I would have no way of knowing over the net, so please take this with a grain of salt.
I have no doubt he has your best interests at heart and you should continue to have faith in your doctor; that said..
Studies conducted as recently as 2017 have demonstrated that Propanolol has roughly a 53% success rate wheras other drugs such as say; "Propafenone" carry a record of success ranging from 66% - 76%.
Of course its all else fails there's always amiodorone which carries with it the low but noteworthy risk of developing some pretty nasty and potentially lethal side effects. You can accepted this risk however in exchange for a success rate of 80%-90%.
Theres also other Beta Blockers such as Sotalol with a cool 60%- 70%.
Limitations: Every study has a different end point, so as such this data was derived from different sources with high degrees of variability. Estimated made based on a 6 month success rate. Afib Recurrence at 1 year is understandably more common.
What is clear however is that Amiodorone, Propafenone and Sotalol are statistically the most effective drugs at rhythm maintenance in AFib.